schedule: fix datarace in operator.check (#8264)

[ti-chi-bot]

This is an automated cherry-pick of #8264

What problem does this PR solve?

Issue Number: Close #8263

What is changed and how does it work?

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)
  go test -timeout 120s -run ^TestOperatorCheckConcurrently$ github.com/tikv/pd/pkg/schedule/operator -race
• in master

==================
WARNING: DATA RACE
Read at 0x00c0004dc240 by goroutine 212:
  github.com/tikv/pd/pkg/schedule/operator.(*Operator).Check()
      /home/lhy1024/pd/pkg/schedule/operator/operator.go:382 +0x5c4
  github.com/tikv/pd/pkg/schedule/operator.TestOperatorCheckConcurrently.func1()
      /home/lhy1024/pd/pkg/schedule/operator/operator_test.go:593 +0xbe

Previous write at 0x00c0004dc240 by goroutine 215:
  sync/atomic.CompareAndSwapInt64()
      /usr/lib/go/src/runtime/race_amd64.s:316 +0xb
  sync/atomic.CompareAndSwapInt64()
      <autogenerated>:1 +0x1a
  github.com/tikv/pd/pkg/schedule/operator.TestOperatorCheckConcurrently.func1()
      /home/lhy1024/pd/pkg/schedule/operator/operator_test.go:593 +0xbe

Goroutine 212 (running) created at:
  github.com/tikv/pd/pkg/schedule/operator.TestOperatorCheckConcurrently()
      /home/lhy1024/pd/pkg/schedule/operator/operator_test.go:591 +0x487
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:1689 +0x21e
  testing.(*T).Run.gowrap1()
      /usr/lib/go/src/testing/testing.go:1742 +0x44

Goroutine 215 (running) created at:
  github.com/tikv/pd/pkg/schedule/operator.TestOperatorCheckConcurrently()
      /home/lhy1024/pd/pkg/schedule/operator/operator_test.go:591 +0x487
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:1689 +0x21e
  testing.(*T).Run.gowrap1()
      /usr/lib/go/src/testing/testing.go:1742 +0x44
==================
--- FAIL: TestOperatorCheckConcurrently (0.00s)
    testing.go:1398: race detected during execution of test
FAIL
FAIL    github.com/tikv/pd/pkg/schedule/operator        0.103s
FAIL

• with this pr

ok      github.com/tikv/pd/pkg/schedule/operator        1.098s

Release note

None.

[ti-chi-bot]

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[ti-chi-bot]

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Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci/build	247158f	link	true	/test build

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[HuSharp]

has been cherry-picked in #8401