flaky test TestMemTracker4InsertAndReplaceExec

[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)

    oom_test.go:108: 
        	Error Trace:	pkg/executor/test/oomtest/oom_test.go:108
        	Error:      	Not equal: 
        	            	expected: ""
        	            	actual  : "background process exited"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-
        	            	+background process exited
        	Test:       	TestMemTracker4InsertAndReplaceExec

    oom_test.go:119: 
        	Error Trace:	pkg/executor/test/oomtest/oom_test.go:119
        	Error:      	Not equal: 
        	            	expected: ""
        	            	actual  : "initialize slot capacity"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-
        	            	+initialize slot capacity
        	Test:       	TestMemTracker4InsertAndReplaceExec

4. What is your TiDB version? (Required)