Fix broken spec for unsubmitted course alerts

I didn't notice that I broke when I changed the TIME_AFTER_CREATION period recently. This updates the spec correspondingly.

spec/lib/alerts/unsubmitted_course_alert_manager_spec.rb

@@ -58,7 +58,7 @@
              submitted: false,
              slug: 'last_minute_course',
              start: 3.days.from_now,
-             created_at: 1.week.ago)
+             created_at: 4.days.ago)
       subject.create_alerts
       expect(Alert.count).to eq(2)
     end