Enable ruff rule PLC0415

[thierry-martinez]

This commit enables ruff rule PLC0415.

Suggested by EarlMilktea: #301 (comment)

[codecov]

Codecov Report

Attention: Patch coverage is 96.77419% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.06%. Comparing base (81b6c0c) to head (15566ec).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
graphix/repr_mixins.py	93.33%	2 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## master #307 +/- ##
==========================================
+ Coverage 79.97% 80.06% +0.08% 
==========================================
Files 35 36 +1 Lines 5398 5397 -1 ==========================================
+ Hits 4317 4321 +4 + Misses 1081 1076 -5 

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[EarlMilktea]

Looks good!