#2592: GitVersion.MsBuild does not set environment variables for GitHub Action

[ThomasPiskol]

This PR includes code changes and tests to fix #2592.

Description

The actual change in src/GitVersion.Core/BuildAgents/GitHubActions.cs is quite small.
Most of the code changes are related to the NUnit tests. I've renamed a few methods, e.g. ExecuteMsBuildTaskInBuildServer to ExecuteMsBuildTaskInAzurePipeline because they are actually testing the Azure Pipelines integration and not a generic build server integration.
Additionally I've added some tests (WriteVersionInfoTaskShouldUpdateBuildNumberInAzurePipeline) to reproduce #2552. Right now these tests are ignored.

Related Issue

#2592

Motivation and Context

Previously the GitHub Action integration was coupled to the setting update-build-number.
This behaviour is not consistent with the other build server integrations and also not intended from my point of view.
Adding the GitVersion environment variables does not change the build number and should be always done independently of update-build-number.

How Has This Been Tested?

• added new automated tests (see below)
• manually tested with a locally created NuGet package of GitVersion.MsBuild which was consumed by a test project.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[arturcic]

I will have a look. Honestly I would prefer to keep the ExecuteMsBuildTaskInBuildServer generic, but I will check the change you did

[ThomasPiskol]

@arturcic Shall I rename ExecuteMsBuildTaskInAzurePipeline back to ExecuteMsBuildTaskInBuildServer ?

[arturcic]

Ok, I had a look now, I would agree we need to have different names for AzurePipelines and got GitHubActions, merging

[mergify]

Thank you @ThomasPiskol for your contribution!