Set academic year to avoid unexpected results

This claims spec was flaky as the returned academic year wasn't always what we expected it to be, now we've defined it, it'll always be the correct academic year.

spec/system/claims/support/schools/claims/create_claim_spec.rb

@@ -1,7 +1,13 @@
 require "rails_helper"
 
 RSpec.describe "Create claim", service: :claims, type: :system do
-  let!(:claim_window) { create(:claim_window, :current) }
+  let(:academic_year) do
+    build(:academic_year,
+          starts_on: Date.parse("1 September 2020"),
+          ends_on: Date.parse("31 August 2021"),
+          name: "2020 to 2021")
+  end
+  let!(:claim_window) { create(:claim_window, :current, academic_year:) }
   let!(:school) { create(:claims_school) }
   let!(:mentor1) { create(:claims_mentor, first_name: "Anne", schools: [school]) }
   let!(:mentor2) { create(:claims_mentor, first_name: "Joe", schools: [school]) }