br: flaky int test br_cache_table

## Bug Report

found checksum mismatch at the end of the test

```
[2024/12/31 12:10:16.758 +08:00] [ERROR] [restore.go:81] ["failed to restore"] [error="failed to validate checksum: [BR:Restore:ErrRestoreChecksumMismatch]restore checksum mismatch"] [errorVerbose="[BR:Restore:ErrRestoreChecksumMismatch]restore checksum mismatch\nfailed to validate checksum\ngithub.com/pingcap/tidb/br/pkg/restore/snap_client.(*SnapClient).execAndValidateChecksum\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/pkg/restore/snap_client/client.go:1129\ngithub.com/pingcap/tidb/br/pkg/restore/snap_client.(*SnapClient).GoValidateChecksum.func1\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/pkg/restore/snap_client/pipeline_items.go:122\ngithub.com/pingcap/tidb/br/pkg/restore/snap_client.concurrentHandleTablesCh.func2\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/pkg/restore/snap_client/pipeline_items.go:92\ngolang.org/x/sync/errgroup.(*Group).Go.func1\n\t/go/pkg/mod/golang.org/x/sync@v0.10.0/errgroup/errgroup.go:78\nruntime.goexit\n\t/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.23.4.linux-amd64/src/runtime/asm_amd64.s:1700"] [stack="github.com/pingcap/tidb/br/cmd/br.runRestoreCommand\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/cmd/br/restore.go:81\ngithub.com/pingcap/tidb/br/cmd/br.newDBRestoreCommand.func1\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/cmd/br/restore.go:200\ngithub.com/spf13/cobra.(*Command).execute\n\t/go/pkg/mod/github.com/spf13/cobra@v1.8.1/command.go:985\ngithub.com/spf13/cobra.(*Command).ExecuteC\n\t/go/pkg/mod/github.com/spf13/cobra@v1.8.1/command.go:1117\ngithub.com/spf13/cobra.(*Command).Execute\n\t/go/pkg/mod/github.com/spf13/cobra@v1.8.1/command.go:1041\ngithub.com/pingcap/tidb/br/cmd/br.main\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/cmd/br/main.go:36\ngithub.com/pingcap/tidb/br/cmd/br.TestRunMain.func1\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/cmd/br/main_test.go:73"]
Error: failed to validate checksum: [BR:Restore:ErrRestoreChecksumMismatch]restore checksum mismatch
[2024/12/31 12:10:16.758 +08:00] [ERROR] [main.go:38] ["br failed"] [error="failed to validate checksum: [BR:Restore:ErrRestoreChecksumMismatch]restore checksum mismatch"] [errorVerbose="[BR:Restore:ErrRestoreChecksumMismatch]restore checksum mismatch\nfailed to validate checksum\ngithub.com/pingcap/tidb/br/pkg/restore/snap_client.(*SnapClient).execAndValidateChecksum\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/pkg/restore/snap_client/client.go:1129\ngithub.com/pingcap/tidb/br/pkg/restore/snap_client.(*SnapClient).GoValidateChecksum.func1\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/pkg/restore/snap_client/pipeline_items.go:122\ngithub.com/pingcap/tidb/br/pkg/restore/snap_client.concurrentHandleTablesCh.func2\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/pkg/restore/snap_client/pipeline_items.go:92\ngolang.org/x/sync/errgroup.(*Group).Go.func1\n\t/go/pkg/mod/golang.org/x/sync@v0.10.0/errgroup/errgroup.go:78\nruntime.goexit\n\t/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.23.4.linux-amd64/src/runtime/asm_amd64.s:1700"] [stack="github.com/pingcap/tidb/br/cmd/br.main\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/cmd/br/main.go:38\ngithub.com/pingcap/tidb/br/cmd/br.TestRunMain.func1\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/cmd/br/main_test.go:73"]

```

mentioned
```
[2024/12/31 12:10:00.530 +08:00] [WARN] [client.go:263] ["Keyspace BR is not supported in this cluster, fallback to legacy restore"] [error="rpc error: code = Unavailable desc = not leader"] [errorVerbose="rpc error: code = Unavailable desc = not leader\ngithub.com/tikv/pd/client.(*client).respForErr\n\t/go/pkg/mod/github.com/tikv/pd/client@v0.0.0-20241220053006-461b86adc78d/client.go:1358\ngithub.com/tikv/pd/client.(*client).GetAllStores\n\t/go/pkg/mod/github.com/tikv/pd/client@v0.0.0-20241220053006-461b86adc78d/client.go:986\ngithub.com/pingcap/tidb/br/pkg/version.CheckClusterVersion\n\t/home/jenkins/agent/workspace/pingcap/tidb/pull_br_integration_test/tidb/br/pkg/version/version.go:90\ngithub.com/pingcap/tidb/br/pkg/restore/snap_client.
```

probably has something to do with it? Need to repro locally