Rollup merge of #119803 - oli-obk:even_more_follow_up_errors, r=compi…

…ler-errors

Silence some follow-up errors [1/x]

this is one piece of the requested cleanups from rust-lang/rust#117449

When we use `-> impl SomeTrait<_>` as a return type, we are both using the "infer return type suggestion" code path, and the infer opaque type code path within the same function. That can lead to confusing diagnostics, so silence all opaque type diagnostics in that case.