`verify_whl` check should explicitly check that `api.md` is not included in the whl

[swathipil]

Currently, *.md files are not included in the whl by default. However, it's still possible that api.md is added accidentally in the MANIFEST.in/pyproject.toml/etc. one day. We want to explicitly check in verify_whl/other relevant checks that the api.md is NOT in the whl.