DM-50244: Make quantum graph generation more permissive about missing init-outputs in --skip-existing-in collections

[TallJimbo]

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 8 lines in your changes missing coverage. Please review.

Project coverage is 82.60%. Comparing base (753c8ce) to head (266af78).

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
python/lsst/pipe/base/quantum_graph_builder.py	50.00%	7 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #487      +/-   ##
==========================================
- Coverage   82.64%   82.60%   -0.04%     
==========================================
  Files         111      111              
  Lines       14355    14367      +12     
  Branches     1844     1846       +2     
==========================================
+ Hits        11863    11868       +5     
- Misses       2041     2047       +6     
- Partials      451      452       +1     

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