Prevent modifying eng/common outside of a re-bootstrap

[MichaelSimons]

The eng/common contents must match the bootstrap arcade version. It would be ideal if there was a mechanism/test that would ensure eng/common contents match the bootstrap arcade.

[ellahathaway]

I think implementing this as a unit test would be beneficial. It would prevent changes to eng/common from being merged unless they match the bootstrap arcade version, while still allowing developers to test changes to eng/common in their local builds.

[ViktorHofer]

A unit test only helps if you run it which we usually only do on CI. Given that, why not just implement this via a simple GH workflow? There are more cases that we want to catch, i.e. modifications to Versions.props / Version.Details files. Those would need to rely on git which isn't great.

Also, we don't want this to be blocking blocking. There should still be an escape hatch (i.e. ignore the GH workflow) if you really know what you are doing.

[ellahathaway]

why not just implement this via a simple GH workflow?

Sure, I can implement it this way. My previous apprehension to using a GH workflow was that dotnet/dotnet was not configured to use them. But now that we've enabled backport flow, the repo is set up to support workflows.