update availability tests with Azure US Gov IPs

Author: mrbullwinkle

articles/azure-monitor/app/ip-addresses.md

@@ -174,6 +174,13 @@ East US
 20.42.35.112/28
 20.42.35.128/28
 
+Azure US Government
+
+20.140.48.160/27
+20.140.56.160/27
+20.140.64.160/27
+20.140.72.160/27
+52.127.49.96/27
 ```  
 
 ## Application Insights & Log Analytics APIs