DEV: Periodically delete old email change requests (#13054)

Email change requests are never deleted no matter if they completed
successfully or not. The abandoned requests have the disadvantage of
showing up as unconfirmed emails in user's preferences page.

spec/jobs/clean_up_email_change_requests_spec.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe Jobs::CleanUpEmailChangeRequests do
+  it "deletes records older than 1 month" do
+    very_old = Fabricate(:email_change_request, updated_at: 32.days.ago)
+    yesterday = Fabricate(:email_change_request, updated_at: 1.day.ago)
+    today = Fabricate(:email_change_request, updated_at: Time.zone.now)
+
+    expect { described_class.new.execute({}) }.to change { EmailChangeRequest.count }.by(-1)
+    expect { very_old.reload }.to raise_error(ActiveRecord::RecordNotFound)
+    expect(yesterday.reload).to be_present
+    expect(today.reload).to be_present
+  end
+end