flaky test TestParallelFlashbackTable

[D3Hunter]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

    db_change_failpoints_test.go:160: 
        	Error Trace:	pkg/ddl/db_change_failpoints_test.go:160
        	            				pkg/ddl/db_change_test.go:1414
        	            				pkg/ddl/db_change_failpoints_test.go:169
        	Error:      	Received unexpected error:
        	            	[schema:1050]Table 't_flashback2' already exists
        	            	github.com/pingcap/errors.AddStack
        	            		external/com_github_pingcap_errors/errors.go:178
        	            	github.com/pingcap/errors.Trace
        	            		external/com_github_pingcap_errors/juju_adaptor.go:15
        	            	github.com/pingcap/tidb/pkg/ddl.(*ddl).DoDDLJob
        	            		pkg/ddl/ddl.go:1323
        	            	github.com/pingcap/tidb/pkg/ddl.(*ddl).RecoverTable
        	            		pkg/ddl/ddl_api.go:3252
        	            	github.com/pingcap/tidb/pkg/executor.(*DDLExec).executeFlashbackTable
        	            		pkg/executor/ddl.go:595
        	            	github.com/pingcap/tidb/pkg/executor.(*DDLExec).Next
        	            		pkg/executor/ddl.go:179
        	            	github.com/pingcap/tidb/pkg/executor/internal/exec.Next
        	            		pkg/executor/internal/exec/executor.go:410
        	            	github.com/pingcap/tidb/pkg/executor.(*ExecStmt).next
        	            		pkg/executor/adapter.go:1238
        	            	github.com/pingcap/tidb/pkg/executor.(*ExecStmt).handleNoDelayExecutor
        	            		pkg/executor/adapter.go:987
        	            	github.com/pingcap/tidb/pkg/executor.(*ExecStmt).handleNoDelay
        	            		pkg/executor/adapter.go:821
        	            	github.com/pingcap/tidb/pkg/executor.(*ExecStmt).Exec
        	            		pkg/executor/adapter.go:585
        	            	github.com/pingcap/tidb/pkg/session.runStmt
        	            		pkg/session/session.go:2289
        	            	github.com/pingcap/tidb/pkg/session.(*session).ExecuteStmt
        	            		pkg/session/session.go:2150
        	            	github.com/pingcap/tidb/pkg/testkit.(*TestKit).ExecWithContext
        	            		pkg/testkit/testkit.go:383
        	            	github.com/pingcap/tidb/pkg/testkit.(*TestKit).Exec
        	            		pkg/testkit/testkit.go:356
        	            	github.com/pingcap/tidb/pkg/ddl_test.testControlParallelExecSQL.func1
        	            		pkg/ddl/db_change_test.go:1399
        	            	github.com/pingcap/tidb/pkg/util.(*WaitGroupWrapper).Run.func1
        	            		pkg/util/wait_group_wrapper.go:157
        	            	runtime.goexit
        	            		src/runtime/asm_amd64.s:1650
        	Test:       	TestParallelFlashbackTable

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

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

master