[MNT] Move release CI to macos-12 image

[szepeviktor]

v11 is not available any more
https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#standard-github-hosted-runners-for-public-repositories

@fkiraly those jobs do not start
https://github.com/sktime/skbase/actions/runs/10212328626

[fkiraly]

I see, thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.16%. Comparing base (306958d) to head (b8068ed).
Report is 52 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #347      +/-   ##
==========================================
- Coverage   85.07%   84.16%   -0.91%     
==========================================
  Files          45       43       -2     
  Lines        3015     3139     +124     
==========================================
+ Hits         2565     2642      +77     
- Misses        450      497      +47     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.