DEV: Replace deprecated queue_jobs site setting in tests (#464)

The #queue_jobs= method on site settings has been deprecated and replaced by Jobs.run_later! and Jobs.run_immediately!. This PR replaces usages in this plugin so we can remove the fallback in core.

spec/integration/invitee_spec.rb

@@ -5,7 +5,7 @@ require "rails_helper"
 describe DiscoursePostEvent::Invitee do
   before do
     freeze_time
-    SiteSetting.queue_jobs = false
+    Jobs.run_immediately!
     SiteSetting.calendar_enabled = true
     SiteSetting.discourse_post_event_enabled = true
   end

spec/integration/topic_spec.rb

@@ -7,7 +7,7 @@ describe Topic do
 
   before do
     freeze_time
-    SiteSetting.queue_jobs = false
+    Jobs.run_immediately!
     SiteSetting.calendar_enabled = true
     SiteSetting.discourse_post_event_enabled = true
   end

spec/requests/invitees_controller_spec.rb

@@ -4,7 +4,7 @@ require "rails_helper"
 module DiscoursePostEvent
   describe InviteesController do
     before do
-      SiteSetting.queue_jobs = false
+      Jobs.run_immediately!
       SiteSetting.calendar_enabled = true
       SiteSetting.discourse_post_event_enabled = true
       sign_in(user)