Fix epel10 external repo for RHEL build tags

Currently rhel10 build tags that have epel10 added use the same external repo 1 as stream10 build tags. This external repo points to http://dl.fedoraproject.org/pub/epel/10/Everything/$arch/. This is the correct repository for stream10, for rhel10 it afaik should be http://dl.fedoraproject.org/pub/epel/10z/Everything/$arch/.