Add a simpler test

tests/ui/traits/non_lifetime_binders/unifying-placeholders-in-query-response-2.current.stderr

@@ -0,0 +1,11 @@
+warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/unifying-placeholders-in-query-response-2.rs:5:12
+   |
+LL | #![feature(non_lifetime_binders)]
+   |            ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/traits/non_lifetime_binders/unifying-placeholders-in-query-response-2.next.stderr

@@ -0,0 +1,11 @@
+warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/unifying-placeholders-in-query-response-2.rs:5:12
+   |
+LL | #![feature(non_lifetime_binders)]
+   |            ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/traits/non_lifetime_binders/unifying-placeholders-in-query-response-2.rs

@@ -0,0 +1,23 @@
+// revisions: current next
+//[next] compile-flags: -Znext-solver
+// check-pass
+
+#![feature(non_lifetime_binders)]
+//~^ WARN the feature `non_lifetime_binders` is incomplete
+
+trait Id {
+    type Output: ?Sized;
+}
+
+impl<T: ?Sized> Id for T {
+    type Output = T;
+}
+
+trait Everyone {}
+impl<T: ?Sized> Everyone for T {}
+
+fn hello() where for<T> <T as Id>::Output: Everyone {}
+
+fn main() {
+    hello();
+}