Ensure seeds don't create session dates outside range

This ensures that when creating a session in the seeds, the date fits
within the range of suitable dates for the current academic year. This
fixes running the tests on the first and last day of the preparation
period.

Author: thomasleese

db/seeds.rb

@@ -88,8 +88,11 @@ def create_session(user, team, programmes:, completed: false, year_groups: nil)
 
   session = FactoryBot.create(:session, date:, team:, programmes:, location:)
 
-  session.session_dates.create!(value: date - 1.day)
-  session.session_dates.create!(value: date + 1.day)
+  [date - 1.day, date + 1.day].each do |value|
+    if value.in?(session.academic_year.to_academic_year_date_range)
+      session.session_dates.create!(value:)
+    end
+  end
 
   programmes.each do |programme|
     year_groups.each do |year_group|