Add :kind test in T7730

testsuite/tests/ghci/scripts/T7730.script

+:set -XPolyKinds
+data A x y
+:i A
+:kind A
+:set -XExistentialQuantification
+data T a = forall a . MkT a
+:info T

testsuite/tests/ghci/scripts/T7730.stdout

+type role A phantom phantom
+data A (x :: k) (y :: k1)
+  	-- Defined at <interactive>:3:1
+A :: k -> k1 -> *
+type role T phantom
+data T (a :: k) where
+  MkT :: forall (k :: BOX) (a :: k) a1. a1 -> T a
+  	-- Defined at <interactive>:7:1