chore(build): Add testing on net48 runtime

[rhysparry]

TL;DR: CI run on Windows testing net48 runtime with netstandard2.0 targetted libraries.

This pull request includes several changes to the CI/CD workflows and the test project configuration to improve compatibility and streamline the build and release processes. The most important changes are grouped by theme below:

CI/CD Workflow Improvements:

• .github/workflows/dotnet-ci-build.yml: Updated the runs-on parameter to use a matrix strategy, allowing the build to run on both ubuntu-latest and windows-latest environments.
• .github/workflows/nuget-publish.yml: Added a new test job that runs on windows-latest and includes steps for checkout, setting up .NET Core 8, installing tools, and running tests. The build job now depends on the test job.

Test Project Configuration:

• Dirt.Args.Tests/Dirt.Args.Tests.csproj: Modified the project file to conditionally target different frameworks based on the operating system. For Windows, it targets both net8.0 and net48, while for other operating systems, it targets net8.0 only.

These changes enhance the flexibility and robustness of the CI/CD process by ensuring compatibility with multiple operating systems and improving the test project's configuration.

chore(build): Add testing on net48 runtime

Resolves: #39

chore: reformat github workflow files

[rhysparry]

This change is part of the following stack:

• chore(build): Add testing on net48 runtime #44 ◀

_{Change managed by git-spice.}