Repair fix_file

[bouweandela]

Description

The preprocessor function fix_file is currently broken if it actually fixes a file, it works fine if no fix is implemented. This pull request:

• Changes the preprocessor function fix_file so its return type is compatible with what is expected by the function esmvalcore.preprocessor.preprocess. In practice, the 4 currently implemented fix_file methods all return paths.
• Updated the code to set the attributes property on the original input file for recording provenance if fixes have been applied.
• Tested with recipe ref/recipe_ref_scatterplot.yml.

Link to documentation:

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Checklist

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• 🧪 The new functionality is relevant and scientifically sound
• 🛠 This pull request has a descriptive title and labels
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• 🧪 and 🛠 Documentation is available
• 🛠 Unit tests have been added
• 🛠 Changes are backward compatible
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[codecov]

Codecov Report

❌ Patch coverage is 64.70588% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.65%. Comparing base (e311187) to head (41d59cd).

Files with missing lines	Patch %	Lines
esmvalcore/cmor/fix.py	64.70%	6 Missing ⚠️

❌ Your patch check has failed because the patch coverage (64.70%) is below the target coverage (100.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2993      +/-   ##
==========================================
- Coverage   95.68%   95.65%   -0.04%     
==========================================
  Files         267      267              
  Lines       15726    15741      +15     
==========================================
+ Hits        15048    15057       +9     
- Misses        678      684       +6     

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