drop webpacker4 from matrix

Author: Judahmeek

.github/workflows/ruby.yml

@@ -18,10 +18,7 @@ jobs:
           # TODO restore testing against JRuby w/ therubyrhino
           # - jruby-9.3.7.0
         gemfile:
-          # These have webpacker:
-          - rails_5.2_no_sprockets_webpacker_4
           - rails_7.0_no_sprockets_shakapacker_6
-          # These don't have webpacker:
           - rails_5.2_no_sprockets
           - rails_5.2_sprockets_3
           - rails_5.2_sprockets_4