[`ruff`] Avoid false positive on `ClassVar` reassignment (`RUF012`) (#21478)
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## Summary
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Fixes #21389
Avoid RUF012 false positives when reassigning a ClassVar
## Test Plan
<!-- How was it tested? -->
Added the new reassignment scenario to
`crates/ruff_linter/resources/test/fixtures/ruff/RUF012.py`.
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Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>
ruff
b1e354bd - [`ruff`] Avoid false positive on `ClassVar` reassignment (`RUF012`) (#21478)
