[PS] Set pester version to v4.3.1

[wing328]

Fixed pester version to fix the following errors due to recent release of pester 5.0:

Starting discovery in 12 files.
Discovery finished in 658ms.
[-] Integration Tests.Pet.CRUD tests 688ms (481ms|207ms)
 ActionPreferenceStopException: The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 ParameterBindingException: Cannot retrieve the dynamic parameters for the cmdlet. The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 at <ScriptBlock>, C:\projects\openapi-generator\samples\client\petstore\powershell\tests\Petstore.Tests.ps1:26
[-] Integration Tests.Pet.Find pets test 138ms (136ms|3ms)
 ActionPreferenceStopException: The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 ParameterBindingException: Cannot retrieve the dynamic parameters for the cmdlet. The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 at <ScriptBlock>, C:\projects\openapi-generator\samples\client\petstore\powershell\tests\Petstore.Tests.ps1:112
[-] Integration Tests.Configuration.Get-PSHostSetting tests 9ms (6ms|3ms)
 ActionPreferenceStopException: The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 ParameterBindingException: Cannot retrieve the dynamic parameters for the cmdlet. The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 at <ScriptBlock>, C:\projects\openapi-generator\samples\client\petstore\powershell\tests\Petstore.Tests.ps1:135
[-] Integration Tests.Configuration.Get-PSUrlFromHostSetting tests 65ms (56ms|9ms)
 ActionPreferenceStopException: The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 ParameterBindingException: Cannot retrieve the dynamic parameters for the cmdlet. The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 at <ScriptBlock>, C:\projects\openapi-generator\samples\client\petstore\powershell\tests\Petstore.Tests.ps1:146
[-] Integration Tests.Configuration.Default header tests 21ms (18ms|3ms)
 ActionPreferenceStopException: The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 ParameterBindingException: Cannot retrieve the dynamic parameters for the cmdlet. The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 at <ScriptBlock>, C:\projects\openapi-generator\samples\client\petstore\powershell\tests\Petstore.Tests.ps1:159
[-] Integration Tests.Configuration.Configuration tests 8ms (5ms|3ms)
 ActionPreferenceStopException: The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 ParameterBindingException: Cannot retrieve the dynamic parameters for the cmdlet. The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 at <ScriptBlock>, C:\projects\openapi-generator\samples\client\petstore\powershell\tests\Petstore.Tests.ps1:166
[-] Integration Tests.PSObject.Create Object from JSON tests 57ms (54ms|3ms)
 ActionPreferenceStopException: The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 ParameterBindingException: Cannot retrieve the dynamic parameters for the cmdlet. The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: Legacy Should syntax (without dashes) is not supported in Pester 5. Please refer to migration guide at: https://pester.dev/docs/migrations/v3-to-v4
 at <ScriptBlock>, C:\projects\openapi-generator\samples\client\petstore\powershell\tests\Petstore.Tests.ps1:182
[+] PSPetApi.Tests.ps1 382ms (18ms|337ms)
[+] PSStoreApi.Tests.ps1 217ms (7ms|191ms)
[+] PSUserApi.Tests.ps1 311ms (16ms|276ms)
[+] ApiResponse.Tests.ps1 81ms (6ms|66ms)
[+] Category.Tests.ps1 74ms (3ms|63ms)
[+] InlineObject.Tests.ps1 157ms (29ms|101ms)

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under.\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
• File the PR against the correct branch: master, 4.3.x, 5.0.x. Default: master.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.