Fix this test on a fast machine

The artificial loop wasn't running for long enough for a context
switch to happen, so the finalizer wasn't getting to run early enough.

testsuite/tests/ghc-regress/ccall/should_run/ffi016.hs

@@ -21,4 +21,4 @@ main = do
   a   <- new (55 :: Int)
   env <- new (66 :: Int)
   fp  <- newForeignPtrEnv finptr env a
-  foldl' (+) 0 [1..500000] `seq` return ()
+  foldl' (+) 0 [1..1000000] `seq` return ()