Mark #12447's test case as expected to pass

This appears to have been fixed at some point between GHC 8.0 and
8.2.

testsuite/tests/ghci/scripts/T12447.stdout

 deferEither @(_ ~ _)
-  :: Deferrable (w2 ~ w1) =>
-     proxy (w2 ~ w1) -> (w2 ~ w1 => r) -> Either String r
+  :: (Typeable w1, Typeable w2) =>
+     proxy (w1 ~ w2) -> ((w1 ~ w2) => r) -> Either String r

testsuite/tests/ghci/scripts/all.T

@@ -245,7 +245,7 @@ test('T12091', [extra_run_opts('-fobject-code')], ghci_script,
 test('T12523', normal, ghci_script, ['T12523.script'])
 test('T12024', normal, ghci_script, ['T12024.script'])
 test('T12158', expect_broken(12158), ghci_script, ['T12158.script'])
-test('T12447', expect_broken(12447), ghci_script, ['T12447.script'])
+test('T12447', normal, ghci_script, ['T12447.script'])
 test('T10249', normal, ghci_script, ['T10249.script'])
 test('T12550', normal, ghci_script, ['T12550.script'])
 test('StaticPtr', normal, ghci_script, ['StaticPtr.script'])