Support Puppet 7

Forcing the locale in acceptance tests isn't pretty but for now it's a
valid workaround. Note that the candlepin DB is already forced to
en_US.UTF-8 but this affects initdb. We may see similar problems in
production, but in general LANG should be matching a system locale.

.github/workflows/ci.yml

@@ -77,3 +77,6 @@ jobs:
         env:
           BEAKER_PUPPET_COLLECTION: ${{ matrix.puppet.collection }}
           BEAKER_setfile: ${{ matrix.setfile.value }}
+          # In Puppet 7 the locale ends up being C.UTF-8 if it isn't passed.
+          # This locale doesn't exist in EL7 and won't be supported either.
+          LANG: en_US.UTF-8

metadata.json

@@ -54,7 +54,7 @@
   "requirements": [
     {
       "name": "puppet",
-      "version_requirement": ">= 5.5.8 < 7.0.0"
+      "version_requirement": ">= 5.5.8 < 8.0.0"
     }
   ]
 }