Remove Ruby 2.6 x Gemfile matrix option

Author: radar

.github/workflows/ruby.yml

@@ -38,6 +38,10 @@ jobs:
           - ruby_version: 2.6
             gemfile: gemfiles/rails_7.gemfile
 
+          # Ruby 2.6.x is not supported by this Gemfile
+          - ruby_version: 2.6
+            gemfile: Gemfile
+
           # JRuby is not supported by Rails 7.0.x
           - ruby_version: jruby
             gemfile: gemfiles/rails_7.gemfile