fix fd leaks and detect them as comprehensively as possible - #5026

✅ 00:05 clone
✅ 02:21 install_dependencies
✅ 00:01 host_info
✅ 00:01 check_config
✅ 00:47 unit_tests
✅ 02:49 integration_systemd
✅ 02:33 integration_fs
✅ 00:01 integration_systemd_rootless
✅ 06:21 integration_fs_rootless