Add regression test for #104916

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

tests/ui/associated-type-bounds/issue-104916.rs

@@ -0,0 +1,14 @@
+#![feature(associated_type_bounds)]
+
+trait B {
+    type AssocType;
+}
+
+fn f()
+where
+    dyn for<'j> B<AssocType: 'j>:,
+    //~^ ERROR: associated type bounds are only allowed in where clauses and function signatures
+{
+}
+
+fn main() {}

tests/ui/associated-type-bounds/issue-104916.stderr

@@ -0,0 +1,8 @@
+error: associated type bounds are only allowed in where clauses and function signatures, not in bounds
+  --> $DIR/issue-104916.rs:9:19
+   |
+LL |     dyn for<'j> B<AssocType: 'j>:,
+   |                   ^^^^^^^^^^^^^
+
+error: aborting due to previous error
+