flaky test TestPartitionTableIndexLookUpReader

[hawkingrei]

Bug Report

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1. Minimal reproduce step (Required)

        	Error:      	Not equal: 
        	            	expected: "[1 1]\n[2 2]\n[11 11]\n"
        	            	actual  : "[11 11]\n[12 12]\n[1 1]\n"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1,4 +1,4 @@
        	            	+[11 11]
        	            	+[12 12]
        	            	 [1 1]
        	            	-[2 2]
        	            	-[11 11]
        	            	 
        	Test:       	TestPartitionTableIndexLookUpReader
        	Messages:   	sql:select * from t where a between 1 and 15 limit 3, args:[]

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

3. What did you see instead (Required)

4. What is your TiDB version? (Required)