Add tests for circuitpython-build-bundles

[Neradoc]

Add tests to the PR build workflow in order to catch errors and malformed bundles.

[jepler]

There's currently a "test" in Actions, but it only checks that the build process exits with a zero status. However, due to some recent issues it appears that we need to check something about the actual content of the .mpy files that are generated.

[jepler]

@FoamyGuy do you have any interest in grabbing this?

[FoamyGuy]

I'll add this to my list to look into. It's got a few things ahead of it so it may be a little bit.

@jepler or @Neradoc do either you have an idea in mind for what kind of validation we'd want to do on the mpy file? The only that come to mind for me are check that the size isn't 0, and maybe try importing it under the unix port though I don't know if that will be possible for every library.