Regression test for references with erroring finalisers

In debug mode if the finaliser of a reference counted object throws an error,
then the `RefTracker` is never released. `checkForgottenRefs` will then report
the reference as forgotten, even though the finaliser ran, though not
successfully. The test that is added in this commit indeed shows this is the
case. The next commit fixes the issue, which should improve the experience of
debugging finalisers that fail.

test-control/Test/Control/RefCount.hs

@@ -28,6 +28,7 @@ tests = testGroup "Control.RefCount" [
     , testProperty "prop_ref_never_released0" prop_ref_never_released0
     , testProperty "prop_ref_never_released1" prop_ref_never_released1
     , testProperty "prop_ref_never_released2" prop_ref_never_released2
+    , testProperty "prop_release_ref_exception" prop_release_ref_exception
 #endif
     ]
 
@@ -176,5 +177,13 @@ expectRefNeverReleased :: RefException -> IO Property
 expectRefNeverReleased RefNeverReleased{} = return (property True)
 expectRefNeverReleased e =
     return (counterexample (displayException e) $ property False)
+
+-- | If a finaliser throws an exception, then the 'RefTracker' is still released
+prop_release_ref_exception :: Property
+prop_release_ref_exception = once $ ioProperty $ do
+    finalised <- newIORef False
+    ref  <- newRef (writeIORef finalised True >> error "oops") TestObject
+    _ <- try @SomeException (releaseRef ref)
+    checkForgottenRefs
 #endif