Fix Docker/Podman test suite image build for rocky9: add python3-devel
so 'pip3 install p4python' can compile its C extension against
Python.h. Broke overnight after a host-level podman/OS package update
on workshop-jenkins.das.perforce.com caused the base image
(rockylinux/rockylinux:9-ubi-init) to be pulled fresh, apparently no
longer bundling Python dev headers the way the previously-cached copy
did. Ubuntu's Dockerfile.ubuntu20/22.base already install the
equivalent python3.5-dev; rocky9 was missing its counterpart.