(PDB-4362) Fix branch check to account for 6.0.x and 6.3.x
(PDB-4362) Fix branch check to account for 6.0.x and 6.3.x

Prior to this commit the 6 series branches were testing upgrades against
the latest released tag off of master instead of the latest tag on the
branch.

puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb