[Multiple issue asignees] fix a few specs

lib/api/entities.rb

@@ -279,7 +279,7 @@ module API
     class IssueBasic < ProjectEntity
       expose :label_names, as: :labels
       expose :milestone, using: Entities::Milestone
-      expose :assignee, :author, using: Entities::UserBasic
+      expose :assignees, :author, using: Entities::UserBasic
 
       expose :user_notes_count
       expose :upvotes, :downvotes

spec/models/merge_request_spec.rb

@@ -88,7 +88,7 @@ describe MergeRequest, models: true do
   end
 
   describe '#assignee_or_author?' do
-    let(:user) { build(:user) }
+    let(:user) { build(:user, id: 1) }
 
     it 'returns true for a user that is assigned to a merge request' do
       subject.assignee = user