Unstable unit test TestStartEtcdTimeout in dataflow engine

[amyangfei]

Which jobs are flaking?

https://github.com/pingcap/tiflow/runs/6548240417?check_suite_focus=true

Which test(s) are flaking?

TestStartEtcdTimeout

Jenkins logs or GitHub Actions link

--- FAIL: TestStartEtcdTimeout (0.01s)
    etcd_test.go:66: 
        	Error Trace:	etcd_test.go:66
        	Error:      	Error message not equal:
        	            	expected: "[DFLOW:ErrMasterStartEmbedEtcdFail]start embed etcd timeout 100ms"
        	            	actual  : "[DFLOW:ErrMasterStartEmbedEtcdFail]failed to start embed etcd: initial cluster test-start-etcd-timeout-1=[http://127.0.0.1:43055,test-start-etcd-timeout-2=http://127.0.0.1:43055](http://127.0.0.1:43055%2Ctest-start-etcd-timeout-2%3Dhttp//127.0.0.1:43055) has duplicate url"
        	Test:       	TestStartEtcdTimeout

Anything else we need to know

• Does this test exist for other branches as well?

• Has there been a high frequency of failure lately?