DEV: Don't user before(:all)/after(:all) (#13389)

Leaking state and non-obvious order (before :all runs *before* RailsHelper.test_setup) are not worth it.
A replacement PR for #13370. Fixes some flaky specs, e.g.
```
bin/rspec './spec/components/freedom_patches/translate_accelerator_spec.rb[1:3]' './spec/jobs/clean_up_user_export_topics_spec.rb[1:1]' --tag ~type:multisite --seed 35994
```

Also included:
* DEV: No need for locale reset (we do it anyway in rails_helper in `test_setup`)

spec/jobs/vacate_legacy_prefix_backups_spec.rb

@@ -1,12 +1,12 @@
 # frozen_string_literal: true
 
 require "s3_helper"
-require 'rails_helper'
+require "rails_helper"
 
 describe Jobs::VacateLegacyPrefixBackups, type: :multisite do
   let(:bucket_name) { "backupbucket" }
 
-  before(:all) do
+  before do
     @s3_client = Aws::S3::Client.new(stub_responses: true)
     @s3_options = { client: @s3_client }
     @objects = []
@@ -15,9 +15,7 @@ describe Jobs::VacateLegacyPrefixBackups, type: :multisite do
     @s3_client.stub_responses(:list_objects_v2, -> (context) do
       { contents: objects_with_prefix(context) }
     end)
-  end
 
-  before do
     setup_s3
     SiteSetting.s3_backup_bucket = bucket_name
     SiteSetting.backup_location = BackupLocationSiteSetting::S3