Tests are failing with new setuptools due to new metadata version

[frenzymadness]

The codebase is not ready for a new metadata version, and instead of using the latest mapping available, it falls back to the empty list here:

pkginfo2/pkginfo2/distribution.py

Lines 121 to 122 in 936ccc2

	def _getHeaderAttrs(self):
	return HEADER_ATTRS.get(self.metadata_version, [])

I think it'd be best to use the latest available mapping instead. If this project is still maintained, I'm willing to open a PR.

[AyanSinhaMahapatra]

@frenzymadness Thanks for pointing this out, please open a PR we would be happy to help you get the fix merged. 😄
We have no intentions of abandoning this project, it just need some love periodically I guess