Add monthly scheduled build (#328)

azure-pipelines.yml

@@ -9,6 +9,16 @@ variables:
 - name: TeamName
   value: Roslyn
 
+schedules:
+  - cron: "0 8 22-28 * 0" # Fourth Sunday of each month at 8:00 UTC
+    displayName: "Monthly build check"
+    branches:
+      include: 
+        - main
+        - release/*
+    always: true # Run even if there have been no source code changes since the last successful scheduled run
+    batch: false # Do not run the pipeline if the previously scheduled run is in-progress
+
 resources:
   repositories:
   - repository: MicroBuildTemplate