Changes

repo-install-test: centos8: fix almalinux keys

Run "dnf upgrade almalinux-release" inside centos8/almalinux8 to upgrade
the gpg keys first, in order to prevent gpg key errors while installing
packages. We are not running repo-install-test for centos8 in CI anymore
(SYS#6759), but I'm currently using this configuration to manually test
that fixing permissions during upgrade and running systemd services as
users works as expected on an rpm-based system.

Related: OS#4107
Related: https://almalinux.org/blog/2023-12-20-almalinux-8-key-update/
Change-Id: Ia06d24ce7ce48651f5a41489e78b5b55dc2d3921