Fix matched effort policy spec for factory bot rails

The change introduced in factory bot rails 6.4.3 impacts this spec.

thoughtbot/factory_bot_rails@0040292#diff-b335630551682c19a781afebcf4d07bf978fb1f8ac04c6bf87428ed5106870f5R168

One we switch to Factory bot Rails > 6.4.3 we began to see Bullet
errors when running this spec.

It's no clear right now if the errors relate to the spec or the code,
but switching all the `build_stubbed` to `create` stops the issue, which
might suggest it is the spec.

Whilst there is a performance hit to using `create` this policy relies
on the `ActivityPolicy` which in turns loads objects from the
database, making stubbing pretty complicated.

For the moment, we will take the perfromance hit for working specs.

spec/policies/matched_effort_policy_spec.rb

@@ -4,13 +4,13 @@
   subject { described_class.new(user, matched_effort) }
 
   let!(:report) { create(:report, :approved, organisation: user.organisation, fund: activity.associated_fund) }
-  let(:matched_effort) { build_stubbed(:matched_effort, activity: activity) }
+  let(:matched_effort) { create(:matched_effort, activity: activity) }
 
   context "as a user that belongs to BEIS" do
-    let(:user) { build_stubbed(:beis_user) }
+    let(:user) { create(:beis_user) }
 
     context "when the activity is a programme activity owned by the organisation" do
-      let(:activity) { build_stubbed(:programme_activity, organisation: user.organisation) }
+      let(:activity) { create(:programme_activity, organisation: user.organisation) }
 
       it "permits all actions" do
         is_expected.to permit_action(:create)
@@ -20,7 +20,7 @@
     end
 
     context "when the activity is a project activity" do
-      let(:activity) { build_stubbed(:project_activity) }
+      let(:activity) { create(:project_activity) }
 
       it "forbids all actions" do
         is_expected.to forbid_action(:create)
@@ -31,10 +31,10 @@
   end
 
   context "as a partner organisation user" do
-    let(:user) { build_stubbed(:partner_organisation_user) }
+    let(:user) { create(:partner_organisation_user) }
 
     context "when the matched effort belongs to an activity owned by the user" do
-      let(:activity) { build_stubbed(:project_activity, organisation: user.organisation) }
+      let(:activity) { create(:project_activity, organisation: user.organisation) }
 
       context "when there is an editable report for the organisation" do
         before do
@@ -58,7 +58,7 @@
     end
 
     context "when the matched effort does not belong to an activity owned by the user" do
-      let(:activity) { build_stubbed(:project_activity) }
+      let(:activity) { create(:project_activity) }
 
       context "when there is an editable report for the organisation" do
         before do