fix: add integer attributes to amend_artifact for explicit unset state

[JonathanPerry651]

This is a bit foul, but it's the only way I could see of actually passing through an explicit False to any of these attrs. I think I need this because junit is coming into my repo as testonly, and I want to amend that to False (I have some other deps that directly depend on junit). If this is the wrong approach for whatever reason, I'm super-open to pushback!

Thank you