[FIX] CSV Import: Fix non-functioning encodings selection

[ales-erjavec]

Issue

CSV Import's Customize Encodings List... does not work on PyQt6. Always clears all except ASCII

Description of changes

Fix check condition due to type mismatch

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.91%. Comparing base (c0c64d6) to head (3f5271a).
⚠️ Report is 148 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7181      +/-   ##
==========================================
+ Coverage   88.82%   88.91%   +0.09%     
==========================================
  Files         335      335              
  Lines       73970    73970              
==========================================
+ Hits        65701    65771      +70     
+ Misses       8269     8199      -70     

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