Fix a bug where the mask_fillvalues preprocessor only recorded provenance for the first result

[bouweandela]

Description

Fix a bug where the mask_fillvalues preprocessor only recorded provenance for the first result. This was introduced in #2340.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.63%. Comparing base (8de26a5) to head (d98849c).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2904   +/-   ##
=======================================
  Coverage   95.63%   95.63%           
=======================================
  Files         263      263           
  Lines       15492    15492           
=======================================
  Hits        14816    14816           
  Misses        676      676           

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[valeriupredoi]

good catch 🐛