[chore] align cosign with opentelemetry-collector-releases

[axw]

Description

See open-telemetry/opentelemetry-collector-releases#1147

Link to tracking issue

Fixes build step errors on all branches that modify cmd/builder, e.g. see https://github.com/open-telemetry/opentelemetry-collector/actions/runs/18304545800/job/52118775447?pr=13838

Testing

N/A

Documentation

N/A

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.66%. Comparing base (2e5abce) to head (175fc82).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13946      +/-   ##
==========================================
- Coverage   91.67%   91.66%   -0.01%     
==========================================
  Files         652      652              
  Lines       42516    42516              
==========================================
- Hits        38978    38974       -4     
- Misses       2730     2733       +3     
- Partials      808      809       +1     

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[axw]

Test failure is unrelated