*: fix data race on the SetResourceGroupTagger

[hawkingrei]

Signed-off-by: Weizhen Wang wangweizhen@pingcap.com

==================
WARNING: DATA RACE
Write at 0x00c001ff5c98 by goroutine 80:
  github.com/tikv/client-go/v2/txnkv/txnsnapshot.(*KVSnapshot).SetResourceGroupTagger()
      /home/prow/go/pkg/mod/github.com/tikv/client-go/v2@v2.0.1-0.20220406091203-f73ec0e675f4/txnkv/txnsnapshot/snapshot.go:756 +0x78a
  github.com/pingcap/tidb/store/driver/txn.(*tikvSnapshot).SetOption()
      /go/tidb/store/driver/txn/snapshot.go:119 +0x73c
  github.com/pingcap/tidb/executor.setOptionForTopSQL()
      /go/tidb/executor/executor.go:2016 +0x67
  github.com/pingcap/tidb/executor.(*PointGetExecutor).Open()
      /go/tidb/executor/point_get.go:197 +0x10eb
  github.com/pingcap/tidb/executor.(*baseExecutor).Open()
      /go/tidb/executor/executor.go:186 +0x2ad
  github.com/pingcap/tidb/executor.(*ProjectionExec).Open()
      /go/tidb/executor/projection.go:86 +0x4b
  github.com/pingcap/tidb/executor.(*UnionExec).resultPuller()
      /go/tidb/executor/executor.go:1660 +0x3d4
  github.com/pingcap/tidb/executor.(*UnionExec).initialize.func1()
      /go/tidb/executor/executor.go:1627 +0x64
Previous write at 0x00c001ff5c98 by goroutine 71:
  github.com/tikv/client-go/v2/txnkv/txnsnapshot.(*KVSnapshot).SetResourceGroupTagger()
      /home/prow/go/pkg/mod/github.com/tikv/client-go/v2@v2.0.1-0.20220406091203-f73ec0e675f4/txnkv/txnsnapshot/snapshot.go:756 +0x78a
  github.com/pingcap/tidb/store/driver/txn.(*tikvSnapshot).SetOption()
      /go/tidb/store/driver/txn/snapshot.go:119 +0x73c
  github.com/pingcap/tidb/executor.setOptionForTopSQL()
      /go/tidb/executor/executor.go:2016 +0x67
  github.com/pingcap/tidb/executor.(*PointGetExecutor).Open()
      /go/tidb/executor/point_get.go:197 +0x10eb
  github.com/pingcap/tidb/executor.(*baseExecutor).Open()
      /go/tidb/executor/executor.go:186 +0x2ad
  github.com/pingcap/tidb/executor.(*ProjectionExec).Open()
      /go/tidb/executor/projection.go:86 +0x4b
  github.com/pingcap/tidb/executor.(*UnionExec).resultPuller()
      /go/tidb/executor/executor.go:1660 +0x3d4
  github.com/pingcap/tidb/executor.(*UnionExec).initialize.func1()
      /go/tidb/executor/executor.go:1627 +0x64
Goroutine 80 (running) created at:
  github.com/pingcap/tidb/executor.(*UnionExec).initialize()
      /go/tidb/executor/executor.go:1627 +0x4d0
  github.com/pingcap/tidb/executor.(*UnionExec).Next()
      /go/tidb/executor/executor.go:1703 +0xc4
  github.com/pingcap/tidb/executor.Next()
      /go/tidb/executor/executor.go:306 +0x5af
  github.com/pingcap/tidb/executor.(*HashAggExec).fetchChildData()
      /go/tidb/executor/aggregate.go:791 +0x319
  github.com/pingcap/tidb/executor.(*HashAggExec).prepare4ParallelExec.func3()
      /go/tidb/executor/aggregate.go:828 +0x64
Goroutine 71 (running) created at:
  github.com/pingcap/tidb/executor.(*UnionExec).initialize()
      /go/tidb/executor/executor.go:1627 +0x4d0
  github.com/pingcap/tidb/executor.(*UnionExec).Next()
      /go/tidb/executor/executor.go:1703 +0xc4
  github.com/pingcap/tidb/executor.Next()
      /go/tidb/executor/executor.go:306 +0x5af
  github.com/pingcap/tidb/executor.(*HashAggExec).fetchChildData()
      /go/tidb/executor/aggregate.go:791 +0x319
  github.com/pingcap/tidb/executor.(*HashAggExec).prepare4ParallelExec.func3()
      /go/tidb/executor/aggregate.go:828 +0x64
==================