Fixes the support for kwargs in `DiscourseEvent.trigger()` on Ruby 3, e.g.
```rb
DiscourseEvent.trigger(:before_system_message_sent, message_type: type, recipient: @recipient, post_creator_args: post_creator_args, params: method_params)
```
Fixes https://github.com/discourse/discourse-local-site-contacts
It's very easy to forget to add `require 'rails_helper'` at the top of every core/plugin spec file, and omissions can cause some very confusing/sporadic errors.
By setting this flag in `.rspec`, we can remove the need for `require 'rails_helper'` entirely.
Jarek Radosz
Phil Pirozhkov
Loïc Guitaut
David Taylor