Fix leader balance blocking region activation #28770

Job	Run time
unit-test (17, windows-latest, others)	24m 46s
unit-test (17, windows-latest, datanode)	31m 45s
unit-test (17, ubuntu-latest, others)	18m 50s
unit-test (17, ubuntu-latest, datanode)	24m 11s
	1h 39m 32s

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