Use repo user to fetch branches

[qwerty287]

closes #4330

[woodpecker-bot]

Deployment of preview was successful: https://woodpecker-ci-woodpecker-pr-4339.surge.sh

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.

Project coverage is 26.55%. Comparing base (bf5405b) to head (017794c).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
server/api/repo.go	0.00%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4339      +/-   ##
==========================================
- Coverage   26.55%   26.55%   -0.01%     
==========================================
  Files         379      379              
  Lines       27548    27555       +7     
==========================================
  Hits         7316     7316              
- Misses      19563    19570       +7     
  Partials      669      669              

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