[Eng] Enable main to be CIed by default (#27135)

* enable main to be CIed by default

* Remove empty line

Author: VeryEarly

.azure-pipelines/azure-powershell-ci.yml

@@ -40,7 +40,10 @@ variables:
 
 trigger:
   batch: true
-
+  branches:
+    include:
+    - main
+  
 jobs:
 - job: Build
   displayName: Build