macos CI: test on push to release branches only (backport #1672)

[mergify]

🦟 Bug fix

Reduces macOS job triggering

Summary

Currently our GitHub workflow for macOS CI runs on every push to a branch, whereas our other CI workflows only run on pushes to release branches. This updates the macOS job triggering to match our Ubuntu CI triggering.

The impact of this change is to reduce the number of CI minutes used and to prevent triggering of duplicate CI jobs (from push and pull_request), potentially reducing the time spent waiting for CI to complete.

Backport Policy

• This is safe to backport to the following versions:
  • Jetty
  • Ionic
  • Harmonic
  • Fortress
• This should not be backported
• I am not sure
• Other (fill in yourself)

Checklist

• Signed all commits for DCO
• Added a screen capture or video to the PR description that demonstrates the fix (as needed)
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• Updated Bazel files (if adding new files). Created an issue otherwise.
• While waiting for a review on your PR, please help review another open pull request to support the maintainers
• Was GenAI used to generate this PR? If so, make sure to add "Generated-by" to your commits. (See this policy for more info.)

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by and Generated-by messages.

Backports: If this is a backport, please use Rebase and Merge instead.

---

This is an automatic backport of pull request #1672 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.50%. Comparing base (6d1a9af) to head (26feb25).
⚠️ Report is 3 commits behind head on sdf14.

Additional details and impacted files

@@           Coverage Diff           @@
##            sdf14    #1679   +/-   ##
=======================================
  Coverage   92.49%   92.50%           
=======================================
  Files         138      138           
  Lines       18451    18535   +84     
=======================================
+ Hits        17066    17145   +79     
- Misses       1385     1390    +5     

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