For docker add --blocking-io only when missing (#19171)

lib/ansible/plugins/action/synchronize.py

@@ -355,8 +355,9 @@ class ActionModule(ActionBase):
         # use rsync_opts to support container to override rsh options
         if self._remote_transport in [ 'docker' ]:
             if not isinstance(self._task.args.get('rsync_opts'), list):
-                self._task.args['rsync_opts'] = []
-            self._task.args['rsync_opts'].append('--blocking-io')
+                self._task.args['rsync_opts'] = self._task.args.get('rsync_opts', '').split(' ')
+            if '--blocking-io' not in self._task.args['rsync_opts']:
+                self._task.args['rsync_opts'].append('--blocking-io')
             if user is not None:
                 self._task.args['rsync_opts'].append("--rsh='%s exec -u %s -i'" % (self._docker_cmd, user))
             else: