24-3: schemeshard: fix crash on concurrent alter-extsubdomains #20452

Job	Run time
check-running-allowed	3s
Build and test relwithdebinfo	2h 8m 50s
Build and test release-asan	2h 16m 24s
Build and test release-clang14	9m 9s
update_integrated_status	3s
	4h 34m 29s

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