ci: centos: run on centos stream 8 image from quay.io
The default centos:latest image can not install packages anymore.
The makecheck-centos test fails with the following error:
$ dnf install -y 'dnf-command(config-manager)'
Error: Failed to download metadata for repo 'appstream'
Cannot prepare internal mirrorlist: No URLs in mirrorlist
Replace it with a centos stream 8 image from quay.io to make the makecheck-centos test pass
Signed-off-by: Uri Lublin uril@redhat.com