Add second test case for #15592

This adds a program from
https://ghc.haskell.org/trac/ghc/ticket/15592#comment:9 (which
briefly refused to typecheck on GHC HEAD) as a test case.

Author: RyanGlScott

testsuite/tests/polykinds/T15592b.hs

@@ -0,0 +1,8 @@
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE TypeFamilies #-}
+module T15592b where
+
+import Data.Kind
+
+class C a where
+  type T (x :: (f :: k -> Type) a)

testsuite/tests/polykinds/T15592b.stderr

@@ -0,0 +1,7 @@
+TYPE CONSTRUCTORS
+  C :: forall {k}. k -> Constraint
+  type role T nominal nominal nominal nominal
+  T :: forall {k} (a :: k) (f :: k -> *). f a -> *
+Dependent modules: []
+Dependent packages: [base-4.12.0.0, ghc-prim-0.5.3,
+                     integer-gmp-1.0.2.0]

testsuite/tests/polykinds/all.T

@@ -194,4 +194,5 @@ test('T15170', normal, compile, [''])
 test('T14939', normal, compile, ['-O'])
 test('T15577', normal, compile_fail, ['-O'])
 test('T15592', normal, compile, [''])
+test('T15592b', normal, compile, ['-ddump-types -fprint-explicit-foralls'])
 test('T15787', normal, compile_fail, [''])