Fix raw HTTP 422 in case head branch is missing on remote

[PawelLipski]

Based on PR #1540

Chain of upstream PRs as of 2025-11-26

• PR Release v3.38.0 #1540:
  master ← develop

  • PR Fix raw HTTP 422 in case head branch is missing on remote #1542 (THIS ONE):
    develop ← fix/422-github-missing-head

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.56%. Comparing base (3be59f4) to head (29c1d90).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1542      +/-   ##
===========================================
- Coverage    98.66%   98.56%   -0.11%     
===========================================
  Files           27       27              
  Lines         4510     4537      +27     
  Branches       854      857       +3     
===========================================
+ Hits          4450     4472      +22     
- Misses          38       42       +4     
- Partials        22       23       +1     

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