[Bug Report] Branch StartMergeBack can't work expectedly

[newborn22]

Overview of the Issue

StartMergeBack cmd will cause error.

  "FailedShards": [
    {
      "Shard": "0",
      "Err": "rpc error: code = Unknown desc = TabletManager.ExecuteQuery on zone1-0000000000 error: rpc error: code = Unauthenticated desc = missing caller id: rpc error: code = Unauthenticated desc = missing caller id"
    }
  ],
  "SuccessShards": [],
  "CurSQLIndex": 0,
  "Sqls": [
    "ALTER TABLE `product` ADD COLUMN `v2` int, ADD COLUMN `v3` int"
  ],
  "UUIDs": null,
  "ExecutorErr": "",
  "TotalTimeSpent": 4546958
}
Branch Error: rpc error: code = Unknown desc = schema change failed, ExecuteResult: {
  "FailedShards": [
    {
      "Shard": "0",
      "Err": "rpc error: code = Unknown desc = TabletManager.ExecuteQuery on zone1-0000000000 error: rpc error: code = Unauthenticated desc = missing caller id: rpc error: code = Unauthenticated desc = missing caller id"
    }
  ],
  "SuccessShards": [],
  "CurSQLIndex": 0,
  "Sqls": [
    "ALTER TABLE `product` ADD COLUMN `v2` int, ADD COLUMN `v3` int"
  ],
  "UUIDs": null,
  "ExecutorErr": "",
  "TotalTimeSpent": 4546958
}
E0926 13:05:31.485242     118 main.go:105] remote error: rpc error: code = Unknown desc = schema change failed, ExecuteResult: {
  "FailedShards": [
    {
      "Shard": "0",
      "Err": "rpc error: code = Unknown desc = TabletManager.ExecuteQuery on zone1-0000000000 error: rpc error: code = Unauthenticated desc = missing caller id: rpc error: code = Unauthenticated desc = missing caller id"
    }
  ],
  "SuccessShards": [],
  "CurSQLIndex": 0,
  "Sqls": [
    "ALTER TABLE `product` ADD COLUMN `v2` int, ADD COLUMN `v3` int"
  ],
  "UUIDs": null,
  "ExecutorErr": "",
  "TotalTimeSpent": 4546958
}

Reproduction Steps

vtctlclient --server localhost:15999 Branch -- --workflow_name branch_test StartMergeBack

Binary Version

code commit hash: 49146bc9c3e817c1e6463628772ca7daded78911

Operating System and Environment details

when wescale connected to wesql.

Log Fragments

No response

[newborn22]

fixed