Add 3.27 to supported-branches (originally 3.26)

[ggainey]

Katello-4.21 wants to use current-releases of plugins - add to supported-branches

[jobselko]

#1139

[jobselko]

We decided to change 3.26 to 3.27 to account for the deprecated publications - #1149

[jobselko]

Publications were deprecated in #1147