Add test for #22238

testsuite/tests/quantified-constraints/T22238.hs

+{-# LANGUAGE ImpredicativeTypes #-}
+{-# LANGUAGE GADTs #-}
+
+module T22238 where
+
+import Data.Kind (Constraint)
+
+data Dict (c :: Constraint) where
+    MkDict :: c => Dict c
+
+forallListEqDict :: Dict (forall a. Eq a => Eq [a])
+forallListEqDict = MkDict

testsuite/tests/quantified-constraints/all.T

@@ -44,3 +44,4 @@ test('T19690', normal, compile_fail, [''])
 test('T23143', normal, compile, [''])
 test('T23333', normal, compile, [''])
 test('T23323', normal, compile, [''])
+test('T22238', normal, compile, [''])