Add a failing rustdoc-ui test for public infinite recursive type

tests/rustdoc-ui/error-in-impl-trait/infinite-recursive-type-2.rs

@@ -0,0 +1,9 @@
+// check-pass
+
+pub fn f() -> impl Sized {
+    pub enum E {
+        V(E),
+    }
+
+    unimplemented!()
+}