## Summary
Fixed false-positive on the rule `PLW1641`, where the explicit
assignment on the `__hash__` method is not counted as an definition of
`__hash__`. (Discussed in #10557).
Also, added one new testcase.
## Test Plan
Checked on `cargo test` in `eq_without_hash.py`.
Before the change, for the assignment into `__hash__`, only `__hash__ =
None` was counted as an explicit definition of `__hash__` method.
Probably any assignment into `__hash__` property could be counted as an
explicit definition of hash, so I removed `value.is_none_literal_expr()`
check.