Mark the AuthorizedProjectsWorker as idempotent

The AuthorizedProjectsWorker is a wrapper around the
`Users::RefreshAuthorizedProjectsService`.

The service itself prevents 2 jobs from running at the same time using
an exclusive lease. And the job itself creates and removes any project
authorizations by recalculating all the authorizations for the given
user using `Gitlab::ProjectAuthorizations`.

Doing this twice will mean the last execution has no effect.

app/workers/all_queues.yml

@@ -856,7 +856,7 @@
   :urgency: :high
   :resource_boundary: :unknown
   :weight: 2
-  :idempotent: 
+  :idempotent: true
 - :name: background_migration
   :feature_category: :not_owned
   :has_external_dependencies: 

app/workers/authorized_projects_worker.rb

 # frozen_string_literal: true
 
-class AuthorizedProjectsWorker # rubocop:disable Scalability/IdempotentWorker
+class AuthorizedProjectsWorker
   include ApplicationWorker
   prepend WaitableWorker
 
@@ -8,6 +8,8 @@ class AuthorizedProjectsWorker # rubocop:disable Scalability/IdempotentWorker
   urgency :high
   weight 2
 
+  idempotent!
+
   # This is a workaround for a Ruby 2.3.7 bug. rspec-mocks cannot restore the
   # visibility of prepended modules. See https://github.com/rspec/rspec-mocks/issues/1231
   # for more details.

spec/workers/authorized_projects_worker_spec.rb

@@ -21,5 +21,22 @@ describe AuthorizedProjectsWorker do
         job.perform(-1)
       end
     end
+
+    it_behaves_like "an idempotent worker" do
+      let(:job_args) { user.id }
+
+      it "does not change authorizations when run twice" do
+        group = create(:group)
+        create(:project, namespace: group)
+        group.add_developer(user)
+
+        # Delete the authorization created by the after save hook of the member
+        # created above.
+        user.project_authorizations.delete_all
+
+        expect { job.perform(user.id) }.to change { user.project_authorizations.reload.size }.by(1)
+        expect { job.perform(user.id) }.not_to change { user.project_authorizations.reload.size }
+      end
+    end
   end
 end