unstable test TestStaleReadPrepare

[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)

    result.go:49: 

        	Error Trace:	testkit/result.go:49

        	            				executor/stale_txn_test.go:1050

        	Error:      	Not equal: 

        	            	expected: "[1 10]\n"

        	            	actual  : ""

        	            	

        	            	Diff:

        	            	--- Expected

        	            	+++ Actual

        	            	@@ -1,2 +1 @@

        	            	-[1 10]

        	            	 

        	Test:       	TestStaleReadPrepare

        	Messages:   	sql:execute s1, args:[]

https://do.pingcap.net/jenkins/blue/organizations/jenkins/pingcap%2Ftidb%2Fghpr_unit_test/detail/ghpr_unit_test/23395/pipeline

4. What is your TiDB version? (Required)