BUG #17013: All RH6 repos are missing repomod.xml.asc files.

The following bug has been logged on the website:

Bug reference:      17013
Logged by:          Andrew Greenwood
Email address:      andrew@agrnwd.com
PostgreSQL version: 10.7
Operating system:   RHEL6
Description:        

This breaks YUM install unless you first install the repo RPM then edits the
.repo file and changed repo_gpgcheck = 0 for all repos.

https://download.postgresql.org/pub/repos/yum/10/redhat/rhel-6.12-x86_64/repodata/