fix: resolve 'origin/gh-pages' is not a commit and a branch cannot be created from it error

[JamesIves]

Description

Resolves an issue where the fallback branch creation is not working.

Testing Instructions

This needs to be validated on a release branch before merging, I will do this tomorrow. This started surfacing in the unit test workflow.

Additional Notes

Related #1701

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.02%. Comparing base (b06fcc8) to head (4f9e9d6).
Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/worktree.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1702      +/-   ##
==========================================
+ Coverage   95.70%   96.02%   +0.31%     
==========================================
  Files           7        7              
  Lines         303      302       -1     
  Branches       83       83              
==========================================
  Hits          290      290              
+ Misses         13       12       -1     

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