schemeshard: fix crash on concurrent alter-extsubdomains (#9201)

[uzhastik]

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[github-actions]

⚪ 2024-10-25 12:39:51 UTC Pre-commit check for 035e68c has started.
⚪ 2024-10-25 12:42:26 UTC Build linux-x86_64-relwithdebinfo is running...
🟢 2024-10-25 13:24:41 UTC Build successful.
⚪ 2024-10-25 13:24:58 UTC Tests are running...
🔴 2024-10-25 14:49:00 UTC Some tests failed, follow the links below.

Test history | Test log

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
14581	13212	0	19	1305	45

[github-actions]

⚪ 2024-10-25 12:40:53 UTC Pre-commit check for 035e68c has started.
⚪ 2024-10-25 12:43:27 UTC Build linux-x86_64-release-clang14 is running...
🟢 2024-10-25 12:52:32 UTC Build successful.

[github-actions]

⚪ 2024-10-25 12:41:41 UTC Pre-commit check for 035e68c has started.
⚪ 2024-10-25 12:44:17 UTC Build linux-x86_64-release-asan is running...
🟢 2024-10-25 13:10:08 UTC Build successful.
⚪ 2024-10-25 13:10:26 UTC Tests are running...
🔴 2024-10-25 15:09:41 UTC Some tests failed, follow the links below.

Test history | Test log

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
10227	10131	0	21	26	49