[CI] Fix `tests/distributed/test_ca_buffer_sharing.py` (#22849)

Signed-off-by: ilmarkov <imarkov@redhat.com>
Co-authored-by: ilmarkov <imarkov@redhat.com>
Co-authored-by: Wentao Ye <44945378+yewentao256@users.noreply.github.com>

vllm/distributed/device_communicators/custom_all_reduce.py

@@ -297,7 +297,7 @@ class CustomAllreduce:
     @staticmethod
     def free_shared_buffer(pointers: list[int],
                            group: Optional[ProcessGroup] = None,
-                           rank: Optional[int] = 0) -> None:
+                           rank: Optional[int] = None) -> None:
         if rank is None:
             rank = dist.get_rank(group=group)
         if ops is not None: