CI: run PR tests on release PRs

[onetechnical]

Summary

We neglected to include running CI-PR tests on pull requests to release branches. This fixes that.

Test Plan

Verify that pull request GitHub Actions tests work on release PRs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 50.50%. Comparing base (8f33ac2) to head (57faf59).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6390      +/-   ##
==========================================
+ Coverage   42.55%   50.50%   +7.95%     
==========================================
  Files         661      654       -7     
  Lines      110771   110673      -98     
==========================================
+ Hits        47136    55894    +8758     
+ Misses      60665    51904    -8761     
+ Partials     2970     2875      -95     

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