test: Add automerge test for witr-feedstock

[ytausch]

Description:

This PR adds an integration test that checks if the automerge prefix is set correctly.

Checklist:

• Pydantic model updated or no update needed

Cross-refs, links to issues, etc:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.67%. Comparing base (214dc89) to head (7fc7d0e).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5341   +/-   ##
=======================================
  Coverage   80.67%   80.67%           
=======================================
  Files         144      144           
  Lines       16914    16914           
=======================================
  Hits        13645    13645           
  Misses       3269     3269           

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