flaky test TestCursorFetchErrorInFetch

[hawkingrei]

Bug Report

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1. Minimal reproduce step (Required)

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

3. What did you see instead (Required)

 --- FAIL: TestCursorFetchErrorInFetch (13.74s)
    conn_stmt_test.go:326: 
        	Error Trace:	pkg/server/conn_stmt_test.go:326
        	Error:      	Received unexpected error:
        	            	[executor:8175]Your query has been cancelled due to exceeding the allowed memory limit for a single SQL query. Please try narrowing your query scope or increase the tidb_mem_quota_query limit and try again.[conn=17163206481289329585]
        	            	github.com/pingcap/errors.AddStack
        	            		external/com_github_pingcap_errors/errors.go:174
        	            	github.com/pingcap/errors.(*Error).GenWithStackByArgs
        	            		external/com_github_pingcap_errors/normalize.go:164
        	            	github.com/pingcap/tidb/pkg/util/sqlkiller.(*SQLKiller).HandleSignal
        	            		pkg/util/sqlkiller/sqlkiller.go:68
        	            	github.com/pingcap/tidb/pkg/util/memory.(*PanicOnExceed).Action
        	            		pkg/util/memory/action.go:172
        	            	github.com/pingcap/tidb/pkg/util/memory.(*Tracker).Consume.func1
        	            		pkg/util/memory/tracker.go:437
        	            	github.com/pingcap/tidb/pkg/util/memory.(*Tracker).Consume
        	            		pkg/util/memory/tracker.go:464
        	            	github.com/pingcap/tidb/pkg/store/copr.(*copIteratorWorker).sendToRespCh
        	            		pkg/store/copr/coprocessor.go:1006
        	            	github.com/pingcap/tidb/pkg/store/copr.(*copIteratorWorker).handleCopResponse
        	            		pkg/store/copr/coprocessor.go:1449
        	            	github.com/pingcap/tidb/pkg/store/copr.(*copIteratorWorker).handleCopPagingResult
        	            		pkg/store/copr/coprocessor.go:1349
        	            	github.com/pingcap/tidb/pkg/store/copr.(*copIteratorWorker).handleTaskOnce
        	            		pkg/store/copr/coprocessor.go:1282
        	            	github.com/pingcap/tidb/pkg/store/copr.(*copIteratorWorker).handleTask
        	            		pkg/store/copr/coprocessor.go:1135
        	            	github.com/pingcap/tidb/pkg/store/copr.(*copIteratorWorker).run
        	            		pkg/store/copr/coprocessor.go:817
        	            	runtime.goexit
        	            		src/runtime/asm_amd64.s:1650
        	Test:       	TestCursorFetchErrorInFetch 

4. What is your TiDB version? (Required)