Added serialTest to test_host_memory_stats (#2314)

This unit test fails when entire test suite is running. Adapting the
change from upstream: pytorch#152454
Fixes test_cuda.py::TestCuda::test_host_memory_stats

Author: BLOrange-AMD

test/test_cuda.py

@@ -162,6 +162,7 @@ def test_pinned_memory_with_cudaregister_multithread(self):
         for thread in threads:
             thread.join()
 
+    @serialTest
     def test_host_memory_stats(self):
         # Helper functions
         def empty_stats():