Auto merge of #129777 - nnethercote:unreachable_pub-4, r=Urgau

Add `unreachable_pub`, round 4

A follow-up to #129732.

r? `@Urgau`

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -3127,7 +3127,7 @@ impl<'o, 'tcx> fmt::Debug for TraitObligationStack<'o, 'tcx> {
     }
 }
 
-pub enum ProjectionMatchesProjection {
+pub(crate) enum ProjectionMatchesProjection {
     Yes,
     Ambiguous,
     No,