Fix a possibly decreasing gc barrier after the first gc fails

[snaury]

Changelog entry

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Changelog category

• Not for changelog (changelog entry is not required)

Description for reviewers

It was discovered that tablets sometimes attempted to decrease a gc barrier, which caused CRIT messages to be logged at storage nodes due to possible protocol violation. This PR makes sure we don't decrease the gc barrier and keep sending at least gen:0 as a barrier.

Fixes #14578.

[github-actions]

⚪ 2025-02-20 11:00:58 UTC Pre-commit check linux-x86_64-relwithdebinfo for 9eb56ed has started.
⚪ 2025-02-20 11:01:02 UTC Artifacts will be uploaded here
⚪ 2025-02-20 11:04:09 UTC ya make is running...
🟡 2025-02-20 12:08:58 UTC Some tests failed, follow the links below. Going to retry failed tests...

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
26386	23779	0	1	2467	139

⚪ 2025-02-20 12:11:38 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-02-20 12:33:24 UTC Tests successful.

Test history | Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
216 (only retried tests)	86	0	0	3	127

🟢 2025-02-20 12:33:33 UTC Build successful.
🟢 2025-02-20 12:33:54 UTC ydbd size 2.1 GiB changed* by -2.1 KiB, which is <= 0 Bytes vs main: OK

ydbd size dash	main: 4d7998d	merge: 9eb56ed	diff	diff %
ydbd size	2 239 406 296 Bytes	2 239 404 136 Bytes	-2.1 KiB	-0.000%
ydbd stripped size	474 530 296 Bytes	474 530 296 Bytes	0 Bytes	0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}

[github-actions]

🟢 2025-02-20 11:04:44 UTC The validation of the Pull Request description is successful.

[github-actions]

⚪ 2025-02-20 14:30:51 UTC Pre-commit check linux-x86_64-release-asan for 9eb56ed has started.
⚪ 2025-02-20 14:32:03 UTC Artifacts will be uploaded here
⚪ 2025-02-20 14:35:06 UTC ya make is running...
🟡 2025-02-20 15:36:21 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet Going to retry failed tests...

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
12188	12087	0	45	19	37

⚪ 2025-02-20 15:37:34 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-02-20 15:50:17 UTC Tests successful.

Test history | Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
156 (only retried tests)	118	0	0	4	34

🟢 2025-02-20 15:50:24 UTC Build successful.
🟢 2025-02-20 15:50:51 UTC ydbd size 3.6 GiB changed* by -5.4 KiB, which is <= 0 Bytes vs main: OK

ydbd size dash	main: 4d7998d	merge: 9eb56ed	diff	diff %
ydbd size	3 895 490 664 Bytes	3 895 485 144 Bytes	-5.4 KiB	-0.000%
ydbd stripped size	1 364 013 408 Bytes	1 364 011 616 Bytes	-1.8 KiB	-0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}