unstable test TestIssue21732

[purelind]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Error:      	Not equal: 
        	            	expected: "[2 2]\n[1 1]\n[3 3]\n"
        	            	actual  : "[1 1]\n[3 3]\n[2 2]\n"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1,4 +1,4 @@
        	            	-[2 2]
        	            	 [1 1]
        	            	 [3 3]
        	            	+[2 2]
        	            	 
        	Test:       	TestIssue21732
        	Messages:   	sql:select * from p use index (idx), args:[]

link https://ci.pingcap.net/blue/organizations/jenkins/tidb-unit-test-hourly/detail/tidb-unit-test-hourly/8353/tests

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

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

[tiancaiamao]

It's just the poor quality test code, not related to the product. Remove 'bug' label.