cdc,tests: unit test `etcdWorkerSuite.TestEtcdSum` is flaky

[pingyu]

Bug Report

1. Describe the bug

=== FAIL: pkg/orchestrator Test (79.94s)

{"level":"warn","ts":"2024-01-03T23:46:30.721843+0800","logger":"etcd-client","caller":"v3@v3.5.10/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc000440c40/127.0.0.1:45169","attempt":0,"error":"rpc error: code = DeadlineExceeded desc = context deadline exceeded"}
{"level":"warn","ts":"2024-01-03T23:47:20.03021+0800","logger":"etcd-client","caller":"v3@v3.5.10/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc001b44700/127.0.0.1:35645","attempt":0,"error":"rpc error: code = Unavailable desc = etcdserver: request timed out"}
{"level":"warn","ts":"2024-01-03T23:47:20.121008+0800","logger":"etcd-client","caller":"v3@v3.5.10/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc000050c40/127.0.0.1:35645","attempt":0,"error":"rpc error: code = Canceled desc = context canceled"}
{"level":"warn","ts":"2024-01-03T23:47:20.120932+0800","logger":"etcd-client","caller":"v3@v3.5.10/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc0007c4e00/127.0.0.1:35645","attempt":0,"error":"rpc error: code = Canceled desc = context canceled"}
{"level":"warn","ts":"2024-01-03T23:47:20.1209+0800","logger":"etcd-client","caller":"v3@v3.5.10/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc000441180/127.0.0.1:35645","attempt":0,"error":"rpc error: code = Canceled desc = context canceled"}
{"level":"warn","ts":"2024-01-03T23:47:20.121119+0800","logger":"etcd-client","caller":"v3@v3.5.10/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc000ecc1c0/127.0.0.1:35645","attempt":0,"error":"rpc error: code = Canceled desc = context canceled"}
{"level":"warn","ts":"2024-01-03T23:47:20.12092+0800","logger":"etcd-client","caller":"v3@v3.5.10/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc0021b8540/127.0.0.1:35645","attempt":0,"error":"rpc error: code = Canceled desc = context canceled"}

----------------------------------------------------------------------
FAIL: etcd_worker_test.go:215: etcdWorkerSuite.TestEtcdSum

etcd_worker_test.go:280:
    c.Check(err, check.IsNil)
... value *errors.withStack = etcdserver: request timed out ("etcdserver: request timed out")

OOPS: 17 passed, 1 FAILED

See https://do.pingcap.net/jenkins/blue/organizations/jenkins/tikv%2Fmigration%2Fpull_unit_test/detail/pull_unit_test/16/pipeline/

2. Minimal reproduce step (Required)

Run unit tests in CI.

3. What did you see instead (Required)

Test failed.

4. What did you expect to see? (Required)

Test succeed.

5. What is your migration tool and TiKV version? (Required)

• TiKV: N/A
• TiKV CDC: [close #381] Add integration tests for Kafka sink #382, 4d33975
• TiKV BR:
• TiKV Online Bulk Load: