Run mypy_primer on pull requests

[sobolevn]

I guess that it is a good idea to run priper, when the source code changes.
This might catch possible regressions in the future.

[hauntsaninja]

Thanks, yeah, running more stuff in CI is a good idea, but I'm not sure what exactly.

When adding or changing projects, the thing that is most valuable is the "full" output (you need the full output because e.g. if you misconfigure and there's zero output, the diff is also zero). But "full" output is very verbose across all 100 projects — maybe we need a primer for primer output :-)

For what it's worth, I usually just test locally with mypy_primer -k new_project --debug.

[hauntsaninja]

#28 (comment) is a good example of needing to see the full output to know things are broken :-)