[tests] Clear ro-heap after ReinitializeStringHashSeed isolate has been disposed

Bug: v8:7464
Change-Id: I522efa3718d04398d2096262a5507b1eb3cfd28a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1611546Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Maciej Goszczycki <goszczycki@google.com>
Cr-Commit-Position: refs/heads/master@{#61496}

test/cctest/heap/test-heap.cc

@@ -6310,8 +6310,8 @@ UNINITIALIZED_TEST(ReinitializeStringHashSeed) {
       CHECK(!context.IsEmpty());
       v8::Context::Scope context_scope(context);
     }
-    ReadOnlyHeap::ClearSharedHeapForTest();
     isolate->Dispose();
+    ReadOnlyHeap::ClearSharedHeapForTest();
   }
 }