refactor(process_commit_message): better type and early return

[bearomorphism]

Description

Checklist

• I have read the contributing guidelines

Code Changes

• Add test cases to all the changes you introduce
• Run poetry all locally to ensure this change passes linter check and tests
• Manually test the changes:
  • Verify the feature/bug fix works as expected in real-world scenarios
  • Test edge cases and error conditions
  • Ensure backward compatibility is maintained
  • Document any manual testing steps performed
• Update the documentation for the changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

@@              Coverage Diff               @@
##             v4-9-0-test    #1542   +/-   ##
==============================================
  Coverage               ?   97.96%           
==============================================
  Files                  ?       58           
  Lines                  ?     2705           
  Branches               ?        0           
==============================================
  Hits                   ?     2650           
  Misses                 ?       55           
  Partials               ?        0           

Flag	Coverage Δ
unittests	97.96% <100.00%> (?)

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