Only point out non-diverging arms for match suggestions Fixes #121144 There is no reason to point at diverging arms, which will always coerce to whatever is the match block's evaluated type. This also removes the suggestion from #106601, since as I pointed out in https://github.com/rust-lang/rust/issues/72634#issuecomment-1946210898 the added suggestion is not firing in the right cases, but instead only when one of the match arms already *actually* evaluates to `()`. r? estebank