Add test for issue-75983

Author: JohnTitor

src/test/ui/traits/trait-alias/issue-75983.rs

@@ -0,0 +1,17 @@
+// check-pass
+
+#![feature(trait_alias)]
+
+struct Bar;
+trait Foo {}
+impl Foo for Bar {}
+
+trait Baz = Foo where Bar: Foo;
+
+fn new() -> impl Baz {
+    Bar
+}
+
+fn main() {
+    let _ = new();
+}