Auto merge of #102257 - cjgillot:let-else-lint, r=dingxiangfei2009

Fix lint scoping for let-else.

The scoping for let-else is inconsistent with HIR nesting.  This creates cases, in `ui/let-else/let-else-allow-unused.rs` for instance, where an `allow` lint attribute does not apply to the bindings created by `let-else`.

This PR is an attempt to correct this.

As there is no lint that currently relies on this, the test for this behaviour is https://github.com/rust-lang/rust/pull/101500.

cc `@dingxiangfei2009` as you filed https://github.com/rust-lang/rust/pull/101894