fix: 🐛 Use commish to make branch unique

[JamesIves]

Description

Resolves issue in #1589. Validated this here: https://github.com/JamesIves/github-sponsors-readme-action/actions/runs/9136595776

Testing Instructions

Use github-pages-deploy-action@releases/v4-flow to validate this.

Additional Notes

N/A

[pathmapper]

Thank you! Confirmed this fixes the issue for me -> https://github.com/kreis-viersen/katasteraemter-gemarkungen-fluren-nrw/actions/runs/9137128938

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 96.32%. Comparing base (1a64cb8) to head (9457c33).

Files	Patch %	Lines
src/worktree.ts	66.66%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1591      +/-   ##
==========================================
- Coverage   97.60%   96.32%   -1.29%     
==========================================
  Files           7        7              
  Lines         292      299       +7     
  Branches       82       83       +1     
==========================================
+ Hits          285      288       +3     
- Misses          7       11       +4     

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