flaky test TestSomeOfStoreUnsupported

[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)

     subscription_test.go:217: 
        	Error Trace:	br/pkg/streamhelper/subscription_test.go:217
        	Error:      	Not equal: 
        	            	expected: 0x2
        	            	actual  : 0x4
        	Test:       	TestSomeOfStoreUnsupported
        	Messages:   	the leader is from different store: some of events not pushed
--- FAIL: TestSomeOfStoreUnsupported (0.00s) 

https://tiprow.hawkingrei.com/view/gs/pingcapprow/pr-logs/pull/pingcap_tidb/52663/fast_test_tiprow/1782248254419767296#1:build-log.txt%3A1547

4. What is your TiDB version? (Required)