Detect enumerate iterations in loop-iterator-mutation

[charliermarsh]

Summary

Closes #12164.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

ℹ️ ecosystem check detected linter changes. (+5 -0 violations, +0 -0 fixes in 4 projects; 50 projects unchanged)

apache/airflow (+1 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview --select ALL

+ airflow/utils/cli.py:150:17: B909 Mutation to loop iterable `full_command` during iteration

python/mypy (+1 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview

+ mypy/typeops.py:949:21: B909 Mutation to loop iterable `proper_types` during iteration

zulip/zulip (+2 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview --select ALL

+ zerver/lib/markdown/nested_code_blocks.py:82:17: B909 Mutation to loop iterable `parent` during iteration
+ zerver/lib/markdown/nested_code_blocks.py:83:17: B909 Mutation to loop iterable `parent` during iteration

pytest-dev/pytest (+1 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview

+ scripts/release.py:54:17: B909 Mutation to loop iterable `lines` during iteration

Changes by rule (1 rules affected)

code	total	+ violation	- violation	+ fix	- fix
B909	5	5	0	0	0

[charliermarsh]

I need to allow assignments to the current key.