Check that `in_debug_impl` pattern is sound

### Description

See https://github.com/rust-lang/rust-clippy/pull/15688#discussion_r2457050332 and the referenced https://github.com/rust-lang/rust-clippy/pull/15688#discussion_r2423067456 suspect one.

Cc @ada4a and @relaxcn 

### Version

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### Additional Labels

_No response_