Improve tests, correctly trigger warnings, and fix output markdown format

[tboby]

WHAT

• Fix the warnings so they actually trigger (Fix warnings so that they actually trigger! #31)
• Fix the latest release output markdown so that it includes correct markdown spacing and list marker
• Port and adapt the integration testing setup from https://github.com/easybuild-org/EasyBuild.PackageReleaseNotes.Tasks (thanks @MangelMaxime !)
• Swap to MSTest (happy to swap back or to any other)

WHY

Tests are good.

This makes it easier for next steps: probably actually addressing the low-hanging fruit issues, binlog parsing tests, and formatting.

[baronfel]

What's the WIP pipeline for?

[tboby]

What's the WIP pipeline for?

It's something fiddly: it's the source you want to set up the nuget.config for your new test folder, but it seemed that if you have it in the pipeline then it can't restore from nuget.org.

See https://github.com/ionide/KeepAChangelog/actions/runs/11494434344/job/31991923809#step:6:206

I thought it was going to be a series of pipeline fixes that I'd squash after but then it worked with one edit...

[baronfel]

Ok, so this is good and you have no more WIP for it?

[tboby]

Ok, so this is good and you have no more WIP for it?

Yup!