Add dotnet-extensions-ai to mentionees list

Author: gewarren

.github/policies/mention-owners.yml

@@ -412,6 +412,7 @@ configuration:
             then:
               - mentionUsers:
                   mentionees:
+                    - dotnet/dotnet-extensions-ai
                     - shyamnamboodiripad
                   replyTemplate: >-
                     Tagging subscribers to this area: ${mentionees}