Reduce queries in spec/requests/api/merge_requests_spec.rb

This reduces the queries from 97137 to 65136 and the query time from
02:04 to 01:27 in spec/requests/api/merge_requests.rb.
Signed-off-by: Rémy Coutable <remy@rymai.me>

spec/support/api/time_tracking_shared_examples.rb

@@ -3,6 +3,8 @@ shared_examples 'an unauthorized API user' do
 end
 
 shared_examples 'time tracking endpoints' do |issuable_name|
+  let(:non_member) { create(:user) }
+
   issuable_collection_name = issuable_name.pluralize
 
   describe "POST /projects/:id/#{issuable_collection_name}/:#{issuable_name}_id/time_estimate" do