add xiaoxu as reviewer (#19097)

Author: xiaoxuqi-ms

.github/pull_request_assignment.yml

@@ -72,12 +72,14 @@
       - leni-msft
       - ruowan
       - jianyexi
+      - xiaoxuqi-ms
 
 
 - rule:
     paths: "specification/@(providerhub|sql|appplatform|deviceupdate|servicelinker)/**"
     reviewers:
       - raych1
+      - xiaoxuqi-ms
 
 - rule:
     paths: "specification/@(security|edgeorder|synapse)/**"
@@ -207,3 +209,4 @@
       - honghr
       - tianxchen-ms
       - tadelesh
+      - xiaoxuqi-ms