[flake8-bugbear] Implement return-in-generator (B901) (#11644)

## Summary

This PR implements the rule B901, which is part of the opinionated rules
of `flake8-bugbear`.

This rule seems to be desired in `ruff` as per
https://github.com/astral-sh/ruff/issues/3758 and
https://github.com/astral-sh/ruff/issues/2954#issuecomment-1441162976.

## Test Plan

As this PR was made closely following the
[CONTRIBUTING.md](8a25531a71/CONTRIBUTING.md),
it tests using the snapshot approach, that is described there.

## Sources

The implementation is inspired by [the original implementation in the
`flake8-bugbear`
repository](d1aec4cbef/bugbear.py (L1092)).
The error message and [test
file](d1aec4cbef/tests/b901.py)
where also copied from there.

The documentation I came up with on my own and needs improvement. Maybe
the example given in
https://github.com/astral-sh/ruff/issues/2954#issuecomment-1441162976
could be used, but maybe they are too complex, I'm not sure.

## Open Questions

- [ ] Documentation. (See above.)

- [x] Can I access the parent in a visitor?

The [original
implementation](d1aec4cbef/bugbear.py (L1100))
references the `yield` statement's parent to check if it is an
expression statement. I didn't find a way to do this in `ruff` and used
the `is_expresssion_statement` field on the visitor instead. What are
your thoughts on this? Is it possible and / or desired to access the
parent node here?

- [x] Is `Option::is_some(...)` -> `...unwrap()` the right thing to do?

Referring to [this piece of
code](9d5a280f71/crates/ruff_linter/src/rules/flake8_bugbear/rules/return_x_in_generator.rs (L91-L96)).
From my understanding, the `.unwrap()` is safe, because it is checked
that `return_` is not `None`. However, I feel like I missed a more
elegant solution that does both in one.

## Other

I don't know a lot about this rule, I just implemented it because I
found it in a
https://github.com/astral-sh/ruff/labels/good%20first%20issue.

I'm new to Rust, so any constructive critisism is appreciated.

---------

Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>

crates/ruff_linter/src/codes.rs

@@ -383,6 +383,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8Bugbear, "033") => (RuleGroup::Stable, rules::flake8_bugbear::rules::DuplicateValue),
         (Flake8Bugbear, "034") => (RuleGroup::Stable, rules::flake8_bugbear::rules::ReSubPositionalArgs),
         (Flake8Bugbear, "035") => (RuleGroup::Stable, rules::flake8_bugbear::rules::StaticKeyDictComprehension),
+        (Flake8Bugbear, "901") => (RuleGroup::Preview, rules::flake8_bugbear::rules::ReturnInGenerator),
         (Flake8Bugbear, "904") => (RuleGroup::Stable, rules::flake8_bugbear::rules::RaiseWithoutFromInsideExcept),
         (Flake8Bugbear, "905") => (RuleGroup::Stable, rules::flake8_bugbear::rules::ZipWithoutExplicitStrict),
         (Flake8Bugbear, "909") => (RuleGroup::Preview, rules::flake8_bugbear::rules::LoopIteratorMutation),