Update sparse_bitmask.py (#56)

src/compressed_tensors/compressors/sparse_bitmask.py

@@ -67,7 +67,7 @@ def compress(self, model_state: Dict[str, Tensor]) -> Dict[str, Tensor]:
                         f"found an existing entry for {key}. The existing entry will "
                         "be replaced."
                     )
-            compressed_dict |= bitmask_dict
+            compressed_dict.update(bitmask_dict)
 
         return compressed_dict