Enable possibly-used-before-assignment and fix a few of them

[aatle]

Type of Changes

	Type
✓	🔨 Refactoring

Description

Original: #9644

Enables possibly-used-before-assignment for the pylint codebase, fixes the errors in two files, and locally disables the rest.
The disabled errors can probably be fixed but would need extra code coverage.

Refs #9637

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.86%. Comparing base (978981d) to head (cfde1e5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9652      +/-   ##
==========================================
- Coverage   95.86%   95.86%   -0.01%     
==========================================
  Files         174      174              
  Lines       18907    18896      -11     
==========================================
- Hits        18125    18114      -11     
  Misses        782      782              

Files	Coverage Δ
pylint/checkers/__init__.py	93.10% <ø> (ø)
...heckers/refactoring/implicit_booleaness_checker.py	100.00% <100.00%> (ø)
pylint/checkers/similar.py	96.23% <100.00%> (-0.06%)	⬇️
pylint/checkers/typecheck.py	96.62% <ø> (ø)
pylint/testutils/_primer/primer.py	96.15% <ø> (ø)

[github-actions]

🤖 According to the primer, this change has no effect on the checked open source code. 🤖🎉

This comment was generated for commit cfde1e5

[Pierre-Sassoulas]

Thank you for the cleanup, congratulation on becoming a pylint contributor :)