Add regression test for rust-lang#60755

Signed-off-by: Yuki Okushi <jtitor@2k36.org>

Author: JohnTitor

tests/ui/traits/alias/issue-60755.rs

@@ -0,0 +1,12 @@
+// check-pass
+
+#![feature(trait_alias)]
+
+struct MyStruct {}
+trait MyFn = Fn(&MyStruct);
+
+fn foo(_: impl MyFn) {}
+
+fn main() {
+    foo(|_| {});
+}