Disable ActiveRecord partial inserts

As mentioned in the Rails pull request [1], the main reason for partial
inserts is no longer relevant thanks to the `ignored_columns` method
(which we haven't even needed so far).

I don't have a preference regarding this setting; we're enabling it in
order to reduce the number of settings we customize.

[1] Pull request 42769 in https://github.com/rails/rails

config/initializers/new_framework_defaults_7_0.rb

@@ -58,7 +58,7 @@ Rails.application.config.active_record.verify_foreign_keys_for_fixtures = true
 # Disable partial inserts.
 # This default means that all columns will be referenced in INSERT queries
 # regardless of whether they have a default or not.
-# Rails.application.config.active_record.partial_inserts = false
+Rails.application.config.active_record.partial_inserts = false
 
 # Protect from open redirect attacks in `redirect_back_or_to` and `redirect_to`.
 # Rails.application.config.action_controller.raise_on_open_redirects = true