Test Rails 7 app against Heroku CI

Added a test for Rails 7 to exercise behavior in #1254. Update the Rails 7 example app to use the released version instead of alpha. Also update the app to be Heroku CI compat app (adds app.json):

- sharpstone/rails-jsbundling@34bd25c
- sharpstone/rails-jsbundling@a98a4e4
- sharpstone/rails-jsbundling@b4ec664
- sharpstone/rails-jsbundling@1fb48b4

Add CI tests against Rails 7

hatchet.lock

@@ -46,7 +46,7 @@
 - - "./repos/rails_versions/active_storage_non_local"
   - 86dddf0127043abba1cb2890590a1d38f111edbd
 - - "./repos/rails_versions/rails-jsbundling"
-  - 192a71e0931aa00724412521dcad4d1e1db2ec0f
+  - 34bd25cef7c09758b3e7763a5d4be6dc94364606
 - - "./repos/rails_versions/rails3_default_ruby"
   - a6b44db674c0d3538633989295e2cfd5e8e1ba0d
 - - "./repos/rails_versions/rails42_default_ruby"

spec/hatchet/rails7_spec.rb

@@ -16,4 +16,11 @@
       end
     end
   end
+
+  it "Works on Heroku CI" do
+    Hatchet::Runner.new("rails-jsbundling").run_ci do |test_run|
+      expect(test_run.output).to match("db:schema:load")
+      expect(test_run.output).to match("db:migrate")
+    end
+  end
 end