Use pytest runner for out-of-tree and OpenBSD system tests in CI
In v9.18, the system:gcc:oraclelinux7:amd64
job will keep using the legacy runner until CentOS 7 EoL (in June 2024) as it has ancient pytest package which isn't supported.
Closes #4246 (closed)
Related #3810
openbsd test run: https://gitlab.isc.org/isc-projects/bind9/-/jobs/3578214
Edited by Nicki Křížek