[Issue multiple assignee] fix specs for banzai

lib/banzai/reference_parser/issue_parser.rb

@@ -28,7 +28,7 @@ module Banzai
           nodes,
           Issue.all.includes(
             :author,
-            :assignee,
+            :assignees,
             {
               # These associations are primarily used for checking permissions.
               # Eager loading these ensures we don't end up running dozens of