Minor followups to RUF052 (#14755)
## Summary
Just some minor followups to the recently merged RUF052 rule, that was
added in bf0fd04:
- Some small tweaks to the docs
- A minor code-style nit
- Some more tests for my peace of mind, just to check that the new
methods on the semantic model are working correctly
I'm adding the "internal" label as this doesn't deserve a changelog
entry. RUF052 is a new rule that hasn't been released yet.
## Test Plan
`cargo test -p ruff_linter`
