Fix ydb/tests to conform py2 syntax

[rosik]

Changelog category

• Not for changelog (changelog entry is not required)

Description for reviewers

• Follow-up for Fix segfault when handling ChangeGroupSizeInUnits during VDisk LocalRecovery #28613

[github-actions]

🟢 2025-11-24 16:05:45 UTC The validation of the Pull Request description is successful.

[github-actions]

⚪ 2025-11-24 16:07:42 UTC Pre-commit check linux-x86_64-relwithdebinfo for 6508bc1 has started.
⚪ 2025-11-24 16:08:00 UTC Artifacts will be uploaded here
⚪ 2025-11-24 16:10:06 UTC ya make is running...
🟡 2025-11-24 16:53:29 UTC Some tests failed, follow the links below. Going to retry failed tests...

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
6758	6616	0	2	130	10

⚪ 2025-11-24 16:53:37 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-11-24 17:07:15 UTC Tests successful.

Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
24 (only retried tests)	16	0	0	0	8

🟢 2025-11-24 17:07:23 UTC Build successful.
🟢 2025-11-24 17:07:41 UTC ydbd size 2.3 GiB changed* by 0 Bytes, which is <= 0 Bytes vs main: OK

ydbd size dash	main: 6b33689	merge: 6508bc1	diff	diff %
ydbd size	2 455 378 776 Bytes	2 455 378 776 Bytes	0 Bytes	0.000%
ydbd stripped size	523 311 256 Bytes	523 311 256 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]

⚪ 2025-11-24 16:08:47 UTC Pre-commit check linux-x86_64-release-asan for 6508bc1 has started.
⚪ 2025-11-24 16:09:03 UTC Artifacts will be uploaded here
⚪ 2025-11-24 16:11:14 UTC ya make is running...
🟡 2025-11-24 16:48:46 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
1852	1833	0	6	6	7

🟢 2025-11-24 16:48:54 UTC Build successful.
🟢 2025-11-24 16:49:17 UTC ydbd size 3.8 GiB changed* by 0 Bytes, which is <= 0 Bytes vs main: OK

ydbd size dash	main: 6b33689	merge: 6508bc1	diff	diff %
ydbd size	4 110 283 112 Bytes	4 110 283 112 Bytes	0 Bytes	0.000%
ydbd stripped size	1 527 801 296 Bytes	1 527 801 296 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}

[Copilot]

Pull request overview

This PR converts Python 3 f-strings to Python 2 compatible string formatting using the % operator, as a follow-up to PR #28613 to ensure Python 2 syntax compliance in test code.

Key changes:

• Replace f-string syntax with % string formatting operator
• Maintain identical error message content and clarity
• Update 11 error message statements across 2 test library files

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
ydb/tests/library/harness/kikimr_runner.py	Convert 1 KeyError f-string to % formatting
ydb/tests/library/clients/kikimr_client.py	Convert 10 RuntimeError f-strings to % formatting

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