Show test summary in CI

[ErikSchierboom]

With Github Actions now supporting Job Summaries, we can leverage this to show the test results in a nice way.
For that, we can use the Test Summary Action: https://github.com/test-summary/action
See https://github.com/test-summary/examples/tree/main/dotnet for how to integrate this with .NET.
Note: we should only do this when run in CI, so the test.ps1 script should detect this (probably via an environment variable, see https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables).

[64J0]

Do you have some specific workflow in mind for this feature @ErikSchierboom ?

[ErikSchierboom]

@64J0 I don't really.