Stop testing on Ruby 2.5

Author: valscion

.github/workflows/ruby.yml

@@ -27,7 +27,7 @@ jobs:
           - rails_5_2_pundit_2
           - rails_6_0_pundit_1
           - rails_6_0_pundit_2
-        ruby-version: [ '2.5', '2.7' ]
+        ruby-version: [ '2.7' ]
         bundler-version: [ '1.11' ]
         include:
           # Include Rails 4.2 / Ruby 2.3 combo