lua: bump metrics module

Bump metrics package submodule. There are 8 new commits, but only
two of them affects Tarantool:
- Add election_leader_idle metric [1];
- test: run log capture tests on a separate server [2];
the other 6 affect documentation and CI/CD scripts of the original repo.
The latter one is required to bump luatest in test-run [3], since
otherwise metrics log capture test fails on a new version.

1. https://github.com/tarantool/metrics/commit/ba9726d9b0cdfb22aa56d852f7fdc7b0aa22756a
2. https://github.com/tarantool/metrics/commit/3370f856efd4172bf24916e66e3846eeb01550a8
3. https://github.com/tarantool/test-run/pull/426

NO_DOC=doc is a part of submodule
NO_TEST=repo runs submodule tests, no new test files are added