Rollup merge of #130343 - Fayti1703:patch-correct-async-block-lint-doc, r=compiler-errors

docs: Enable required feature for 'closure_returning_async_block' lint

Failing to do this results in the lint example output complaining about the lint not existing instead of the thing the lint is supposed to be complaining about.

See <https://doc.rust-lang.org/rustc/lints/listing/allowed-by-default.html#closure-returning-async-block>:
![image](https://github.com/user-attachments/assets/78bae16f-3fb6-4d6d-b8aa-768b477cd187)

Author: fmease