Add generic parameters mismatch tests for async in traits

Author: spastorino

tests/ui/async-await/in-trait/generics-mismatch.current.stderr

@@ -0,0 +1,16 @@
+error[E0053]: method `foo` has an incompatible generic parameter for trait `Foo`
+  --> $DIR/generics-mismatch.rs:13:18
+   |
+LL | trait Foo {
+   |       ---
+LL |     async fn foo<T>();
+   |                  - expected type parameter
+...
+LL | impl Foo for () {
+   | ---------------
+LL |     async fn foo<const N: usize>() {}
+   |                  ^^^^^^^^^^^^^^ found const parameter of type `usize`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0053`.

tests/ui/async-await/in-trait/generics-mismatch.next.stderr

@@ -0,0 +1,16 @@
+error[E0053]: method `foo` has an incompatible generic parameter for trait `Foo`
+  --> $DIR/generics-mismatch.rs:13:18
+   |
+LL | trait Foo {
+   |       ---
+LL |     async fn foo<T>();
+   |                  - expected type parameter
+...
+LL | impl Foo for () {
+   | ---------------
+LL |     async fn foo<const N: usize>() {}
+   |                  ^^^^^^^^^^^^^^ found const parameter of type `usize`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0053`.

tests/ui/async-await/in-trait/generics-mismatch.rs

@@ -0,0 +1,17 @@
+// edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
+
+#![feature(async_fn_in_trait)]
+#![allow(incomplete_features)]
+
+trait Foo {
+    async fn foo<T>();
+}
+
+impl Foo for () {
+    async fn foo<const N: usize>() {}
+    //~^ ERROR: method `foo` has an incompatible generic parameter for trait `Foo` [E0053]
+}
+
+fn main() {}