github/workflows: Replace CentOS 8 with Rocky Linux
github/workflows: Replace CentOS 8 with Rocky Linux

CentOS 8 went EOL December 31st 2021 and this workflow now fails with

  Run yum -y install git gcc make jansson-devel libcurl-devel
  CentOS Linux 8 - AppStream                      192  B/s |  38  B     00:00
  Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist

Use Rocky Linux 8 instead, this is another RHEL clone that came about
after the Red Hat notice about CentOS Stream.

Signed-off-by: Andrew Clayton <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@digital-domain.net>

ac000/libac