Use pytest runner for out-of-tree and OpenBSD system tests in CI

Tom Krizek requested to merge 4246-remove-legacy-test-runner-from-ci into main

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:

Edited by Tom Krizek

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