auth-4.7.x: Backport removal of centos-8 and centos-8-stream as build targets

[romeroalx]

Short description

As part of #14241, centos-8 and centos-8-stream were removed from master. Only that commit is backported as part of this PR.

Centos 8 Stream became end-of-builds on May 31st and was only used for daily builds but not for the actual building of packages.

This fixes the CI daily builds: https://github.com/PowerDNS/pdns/actions/runs/9475615358

Checklist

I have:

• [x] read the CONTRIBUTING.md document
• [ ] compiled this code
• [x] tested this code
• [ ] included documentation (including possible behaviour changes)
• [ ] documented the code
• [ ] added or modified regression test(s)
• [ ] added or modified unit test(s)
• [ ] checked that this code was merged to master