Resolved locks not being released before shutdown which causes acquir…

…e lock to block indefinitely.

 -  RPYC_BIND_THREADS=false taskset -c 0 pyenv exec python -m unittest discover -v  -k test_race -k test_refcount -k test_affinity -k test_deploy
 -  RPYC_BIND_THREADS=true taskset -c 0 pyenv exec python -m unittest discover -v  -k test_race -k test_refcount -k test_affinity -k test_deploy

rpyc/core/protocol.py

@@ -222,7 +222,7 @@ def close(self):  # IO
             self._closed = True
             if self._config.get("before_closed"):
                 self._config["before_closed"](self.root)
-            self._async_request(consts.HANDLE_CLOSE)
+            self.sync_request(consts.HANDLE_CLOSE)
         except EOFError:
             pass
         except Exception: