Specialization involving RPITITs is broken so ignore the diagnostic differences for them

Author: spastorino

Diff for: tests/ui/async-await/in-trait/dont-project-to-specializable-projection.stderr renamed to tests/ui/async-await/in-trait/dont-project-to-specializable-projection.current.stderr

@@ -1,5 +1,5 @@
 warning: the feature `async_fn_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/dont-project-to-specializable-projection.rs:4:12
+  --> $DIR/dont-project-to-specializable-projection.rs:6:12
    |
 LL | #![feature(async_fn_in_trait)]
    |            ^^^^^^^^^^^^^^^^^
@@ -8,7 +8,7 @@ LL | #![feature(async_fn_in_trait)]
    = note: `#[warn(incomplete_features)]` on by default
 
 error: async associated function in trait cannot be specialized
-  --> $DIR/dont-project-to-specializable-projection.rs:14:5
+  --> $DIR/dont-project-to-specializable-projection.rs:16:5
    |
 LL |     default async fn foo(_: T) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Diff for: tests/ui/async-await/in-trait/dont-project-to-specializable-projection.next.stderr

@@ -0,0 +1,34 @@
+warning: the feature `async_fn_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/dont-project-to-specializable-projection.rs:6:12
+   |
+LL | #![feature(async_fn_in_trait)]
+   |            ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0053]: method `foo` has an incompatible type for trait
+  --> $DIR/dont-project-to-specializable-projection.rs:16:35
+   |
+LL |     default async fn foo(_: T) -> &'static str {
+   |                                   ^^^^^^^^^^^^ expected associated type, found future
+   |
+note: type in trait
+  --> $DIR/dont-project-to-specializable-projection.rs:12:27
+   |
+LL |     async fn foo(_: T) -> &'static str;
+   |                           ^^^^^^^^^^^^
+   = note: expected signature `fn(_) -> impl Future<Output = &'static str>`
+              found signature `fn(_) -> impl Future<Output = &'static str>`
+
+error: async associated function in trait cannot be specialized
+  --> $DIR/dont-project-to-specializable-projection.rs:16:5
+   |
+LL |     default async fn foo(_: T) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: specialization behaves in inconsistent and surprising ways with `#![feature(async_fn_in_trait)]`, and for now is disallowed
+
+error: aborting due to 2 previous errors; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0053`.

Diff for: tests/ui/async-await/in-trait/dont-project-to-specializable-projection.rs

@@ -1,5 +1,7 @@
 // edition: 2021
 // known-bug: #108309
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![feature(min_specialization)]