bbatsov/rubocop

### Bug fixes

* [#12068](https://github.com/rubocop/rubocop/pull/12068): Fix a false positive for `Style/ReturnNilInPredicateMethodDefinition` when the last method argument in method definition is `nil`. ([@koic][])
* [#12082](https://github.com/rubocop/rubocop/issues/12082): Fix an error for `Lint/UselessAssignment` when a variable is assigned and unreferenced in `for` with multiple variables. ([@koic][])
* [#12079](https://github.com/rubocop/rubocop/issues/12079): Fix an error for `Style/MixinGrouping` when mixin method has no arguments. ([@koic][])
* [#11637](https://github.com/rubocop/rubocop/pull/11637): Correct Rubocop for `private_class_method` method documentation. ([@bigzed][])
* [#12070](https://github.com/rubocop/rubocop/pull/12070): Fix false positive in `Style/ArgumentsForwarding` when receiver forwards args/kwargs. ([@owst][])

[@koic]: https://github.com/koic
[@bigzed]: https://github.com/bigzed
[@owst]: https://github.com/owst