Coercible: Test case for now broken(?) corner case

involving a non-terminating newtype. This worked before 7e78faf0.
Probably not a problem, but still better to have a test case for it. See
ticket #9117.

testsuite/tests/typecheck/should_compile/T9117_2.hs

+module T9117_2 where
+
+
+import Data.Coerce
+
+newtype Foo a = Foo (Foo a)
+newtype Age = MkAge Int
+
+ex1 :: (Foo Age) -> (Foo Int)
+ex1 = coerce

testsuite/tests/typecheck/should_compile/all.T

@@ -419,3 +419,4 @@ test('T8762', normal, compile, [''])
 test('MutRec', normal, compile, [''])
 test('T8856', normal, compile, [''])
 test('T9117', normal, compile, [''])
+test('T9117_2', expect_broken('9117'), compile, [''])