Enable connecting multiple list Attributes

[servantftransperfect]

Enable the connection of multiple listAttributes to the same destination listAttribute

[codecov]

Codecov Report

❌ Patch coverage is 87.77778% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.08%. Comparing base (912a71d) to head (35cf5ba).
⚠️ Report is 3 commits behind head on develop.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
meshroom/core/graph.py	68.57%	11 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3000      +/-   ##
===========================================
+ Coverage    82.01%   82.08%   +0.06%     
===========================================
  Files           69       69              
  Lines         9310     9400      +90     
===========================================
+ Hits          7636     7716      +80     
- Misses        1674     1684      +10     

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[cbentejac]

This seems to work correctly, including when performing undos and redos, but some unit tests should definitely be added.