MGT-python 1.12.1

Fixed

• The contact-sheet test fixture used os.link, which cannot cross drives on Windows, so CI
  failed on all three Windows jobs. Test-only: the 1.12.0 package is correct and this changes
  nothing a user runs. It is released because the v1.12.0 tag points at a commit whose CI is
  red, and a tag that fails its own checks is misleading whatever the wheel contains.

Changed

• The PyPI publish workflow now refuses to run unless CI succeeded on the exact commit being
  released. Publishing fires on a published release, which was independent of CI, which is how
  1.12.0 went out from a red commit in the first place.