This is an attempt to fix the flaky:
```
1) Jobs::Onceoff can run all once off jobs without errors
Failure/Error: self.locale_no_cache = value
I18n::InvalidLocale:
:bar is not a valid locale
# ./lib/freedom_patches/translate_accelerator.rb:193:in `locale='
# ./app/jobs/onceoff/clean_up_user_export_topics.rb:7:in `block in execute_onceoff'
# ./app/jobs/onceoff/clean_up_user_export_topics.rb:6:in `map'
# ./app/jobs/onceoff/clean_up_user_export_topics.rb:6:in `execute_onceoff'
# ./spec/integrity/onceoff_integrity_spec.rb:13:in `block (3 levels) in <main>'
# ./spec/integrity/onceoff_integrity_spec.rb:12:in `each'
# ./spec/integrity/onceoff_integrity_spec.rb:12:in `block (2 levels) in <main>'
```
This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
Since rspec-rails 3, the default installation creates two helper files:
* `spec_helper.rb`
* `rails_helper.rb`
`spec_helper.rb` is intended as a way of running specs that do not
require Rails, whereas `rails_helper.rb` loads Rails (as Discourse's
current `spec_helper.rb` does).
For more information:
https://www.relishapp.com/rspec/rspec-rails/docs/upgrade#default-helper-files
In this commit, I've simply replaced all instances of `spec_helper` with
`rails_helper`, and renamed the original `spec_helper.rb`.
This brings the Discourse project closer to the standard usage of RSpec
in a Rails app.
At present, every spec relies on loading Rails, but there are likely
many that don't need to. In a future pull request, I hope to introduce a
separate, minimal `spec_helper.rb` which can be used in tests which
don't rely on Rails.
