[eas-cli] use branch mapping utility fn

[quinlanj]

Why

Fix a TODO in the codebase to move branch mapping logic to utility function

Test Plan

• tests still pass
• manually sanity tested

[github-actions]

Size Change: -4.72 kB (0%)

Total Size: 51.5 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	51.5 MB	-4.72 kB (0%)

_{compressed-size-action}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e9064b7) 54.11% compared to head (dd43df6) 54.11%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2186   +/-   ##
=======================================
  Coverage   54.11%   54.11%           
=======================================
  Files         516      516           
  Lines       18815    18815           
  Branches     3771     3771           
=======================================
  Hits        10179    10179           
  Misses       8615     8615           
  Partials       21       21           

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

[quinlanj]

/changelog-entry chore use branch mapping utility fn

[github-actions]

✅ Thank you for adding the changelog entry!