fix memory leak in ymq proxy

[siarheivesialou]

A bunch of tests ydb/core/http_proxy/ut/inside_ydb_ut/TestHttpProxy.* was failing under asan, this PR fixes it.

[github-actions]

⚪ 2024-09-04 07:31:32 UTC Pre-commit check linux-x86_64-relwithdebinfo for 46d8160 has started.
⚪ 2024-09-04 07:34:11 UTC ya make is running...
🟡 2024-09-04 08:34:03 UTC Some tests failed, follow the links below. Going to retry failed tests...

Test history | Ya make output

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
14327	12941	0	2	1361	23

⚪ 2024-09-04 08:35:18 UTC ya make is running... (failed tests rerun, try 2)
🟢 2024-09-04 08:42:38 UTC Tests successful.

Test history | Ya make output

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
34 (only retried tests)	17	0	0	1	16

🟢 2024-09-04 08:42:45 UTC Build successful.
🟢 2024-09-04 08:43:17 UTC ydbd size 8.3 GiB changed* by +16.8 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: b666aa2	merge: 46d8160	diff	diff %
ydbd size	8 918 849 008 Bytes	8 918 866 176 Bytes	+16.8 KiB	+0.000%
ydbd stripped size	481 836 328 Bytes	481 838 088 Bytes	+1.7 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}

[github-actions]

⚪ 2024-09-04 07:33:22 UTC Pre-commit check linux-x86_64-release-clang14 for 46d8160 has started.
⚪ 2024-09-04 07:36:06 UTC ya make is running...
🟢 2024-09-04 07:41:19 UTC Build successful.

[github-actions]

⚪ 2024-09-04 07:34:15 UTC Pre-commit check linux-x86_64-release-asan for 46d8160 has started.
⚪ 2024-09-04 07:37:08 UTC ya make is running...
🔴 2024-09-04 09:27:17 UTC Some tests failed, follow the links below.

Test history | Ya make output

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
9904	9776	0	51	46	31

🟢 2024-09-04 09:28:09 UTC Build successful.
🟢 2024-09-04 09:28:44 UTC ydbd size 5.5 GiB changed* by -21.6 KiB, which is <= 0 Bytes vs main: OK

ydbd size dash	main: e43c2fc	merge: 46d8160	diff	diff %
ydbd size	5 954 835 944 Bytes	5 954 813 848 Bytes	-21.6 KiB	-0.000%
ydbd stripped size	1 489 549 744 Bytes	1 489 546 096 Bytes	-3.6 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}