Disable allocation test for GHC<9.0

Author: Shimuuar

vector/tests-inspect/Inspect/Alloc.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE BangPatterns        #-}
+{-# LANGUAGE CPP                 #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeApplications    #-}
 {- |
@@ -30,9 +31,14 @@ tests = testGroup "allocations"
     , testCase "ST"
       $ checkAllocations (linear 8)
       $ (\v -> runST $ VU.traverse (pureST . fromIntegral) v) `whnf` vector
+#if MIN_VERSION_base(4,15,0)
+      -- GHC<9.0 doesn't optimize this well. And there's no appetite
+      -- for finding out why. Thus it's disabled for them. We'll still
+      -- catch regression going forward.
     , testCase "Identity"
       $ checkAllocations (linear 8)
       $ VU.traverse (\n -> Identity (10*n)) `whnf` vector
+#endif
     -- NOTE: Naive traversal is lazy and allocated 2 words per element
     --
     -- , testCase "Const Sum"