flaky test TestStoreGlobalConfig

[hawkingrei]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

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

3. What did you see instead (Required)

    globalconfig_test.go:106: 

        	Error Trace:	/tmp/TestStoreGlobalConfig1514861705/001/globalconfig_test.go:106

        	Error:      	Not equal: 

        	            	expected: "/global/config/source_id"

        	            	actual  : "/global/config/enable_resource_metering"

        	            	

        	            	Diff:

        	            	--- Expected

        	            	+++ Actual

        	            	@@ -1 +1 @@

        	            	-/global/config/source_id

        	            	+/global/config/enable_resource_metering

        	Test:       	TestStoreGlobalConfig

``
### 4. What is your TiDB version? (Required)

<!-- Paste the output of SELECT tidb_version() -->

[Defined2014]

Seems the test already modified by #40955, so close this issue first.