flaky test TestTopNFallBackAction

[hawkingrei]

Bug Report

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3. What did you see instead (Required)

     topn_spill_test.go:209: 
        	Error Trace:	pkg/executor/sortexec/topn_spill_test.go:209
        	            				pkg/executor/sortexec/topn_spill_test.go:519
        	Error:      	Received unexpected error:
        	            	panic is triggered by random fail
        	            	github.com/pingcap/tidb/pkg/util.GetRecoverError
        	            		pkg/util/util.go:290
        	            	github.com/pingcap/tidb/pkg/executor/sortexec.processPanicAndLog
        	            		pkg/executor/sortexec/sort_util.go:50
        	            	github.com/pingcap/tidb/pkg/executor/sortexec.(*TopNExec).executeTopN.func1
        	            		pkg/executor/sortexec/topn.go:449
        	            	runtime.gopanic
        	            		GOROOT/src/runtime/panic.go:914
        	            	github.com/pingcap/tidb/pkg/executor/sortexec.injectParallelSortRandomFail
        	            		pkg/executor/sortexec/sort_util.go:73
        	            	github.com/pingcap/tidb/pkg/executor/sortexec.(*TopNExec).generateResultWithMultiWayMerge
        	            		pkg/executor/sortexec/topn.go:519
        	            	github.com/pingcap/tidb/pkg/executor/sortexec.(*TopNExec).generateTopNResultsWhenSpillTriggered
        	            		pkg/executor/sortexec/topn.go:576
        	            	github.com/pingcap/tidb/pkg/executor/sortexec.(*TopNExec).generateTopNResults
        	            		pkg/executor/sortexec/topn.go:593
        	            	github.com/pingcap/tidb/pkg/executor/sortexec.(*TopNExec).executeTopN
        	            		pkg/executor/sortexec/topn.go:473
        	            	runtime.goexit
        	            		src/runtime/asm_a

https://tiprow.hawkingrei.com/view/gs/pingcapprow/pr-logs/pull/pingcap_tidb/54514/fast_test_tiprow/1838866841766727680#1:build-log.txt%3A2137

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