Add test for rust-lang#66312

Closes rust-lang#66312. This issue was fixed by rust-lang#68884.

src/test/ui/async-await/issue-66312.rs

@@ -0,0 +1,14 @@
+// edition:2018
+
+trait Test<T> {
+    fn is_some(self: T); //~ ERROR invalid `self` parameter type
+}
+
+async fn f() {
+    let x = Some(2);
+    if x.is_some() {
+        println!("Some");
+    }
+}
+
+fn main() {}

src/test/ui/async-await/issue-66312.stderr

@@ -0,0 +1,12 @@
+error[E0307]: invalid `self` parameter type: T
+  --> $DIR/issue-66312.rs:4:22
+   |
+LL |     fn is_some(self: T);
+   |                      ^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0307`.