Replace GitHub Actions weekly workflow with Azure pipeline schedule

Co-authored-by: eleanorjboyd <26030610+eleanorjboyd@users.noreply.github.com>

Author: Copilot

.github/workflows/weekly-build.yml

@@ -1,8 +1,15 @@
-# Run on a schedule
+# Run on a schedule and weekly
 trigger:
   branches:
     include:
       - main
+schedules:
+  - cron: "0 0 * * 0"
+    displayName: Weekly build
+    branches:
+      include:
+        - main
+    always: true
 pr: none
 
 resources: