Update pull_request_assignment.yml (#20012)

Added assignment for two new rps onboarded to shiftleft

Author: raych1

.github/pull_request_assignment.yml

@@ -71,7 +71,7 @@
 
 
 - rule:
-    paths: "specification/@(providerhub|sql|appplatform|deviceupdate|servicelinker)/**"
+    paths: "specification/@(providerhub|sql|appplatform|deviceupdate|servicelinker|imagebuilder|throttling)/**"
     reviewers:
       - raych1
       - xiaoxuqi-ms