Test actiontext on Rails 6.0

- config.load_defaults 6.0 in the dummy app and
  fix the test since by default rails 6.0 configured
  does not generate "utf8" hidden input, see #32125
- Use `ActiveRecord::Migration[6.0]` in the dummy app
  since actiontext will be since Rails 6.0
- Fix `CreateActiveStorageTables` migration in the dummy app.
  Add `t.foreign_key :active_storage_blobs, column: :blob_id`
  It was added in 2ae3a29508e.
- `rails/actiontext$ yarn install`

1 files changed, 1 insertions, 0 deletions

diff --git a/actionmailbox/test/dummy/db/migrate/20180212164506_create_active_storage_tables.active_storage.rb b/actionmailbox/test/dummy/db/migrate/20180212164506_create_active_storage_tables.active_storage.rb
index 360e0d1b7a..0b2ce257c8 100644
--- a/actionmailbox/test/dummy/db/migrate/20180212164506_create_active_storage_tables.active_storage.rb
+++ b/actionmailbox/test/dummy/db/migrate/20180212164506_create_active_storage_tables.active_storage.rb
@@ -21,6 +21,7 @@ class CreateActiveStorageTables < ActiveRecord::Migration[5.2]
       t.datetime :created_at, null: false
 
       t.index [ :record_type, :record_id, :name, :blob_id ], name: "index_active_storage_attachments_uniqueness", unique: true
+      t.foreign_key :active_storage_blobs, column: :blob_id
     end
   end
 end