CI: Add a weekly scheduled run to the Azure pipelines

This commit adds a weekly scheduled run to the Azure pipelines CI. It runs each Monday at 06:00 UTC on the main and maintenance/0.13.x branches.

Periodically scheduled runs can detect errors and warnings appearing in changes in upstream dependencies or the build environment. By having a scheduled run they can be traced back easier to a dependency or environment change, then if they would pop up in a random PR.

Author: EwoutH

azure-pipelines.yml

@@ -2,6 +2,12 @@
 
 trigger:
 - main
+schedules:
+- cron: "0 6 * * 1"   # Each Monday at 06:00 UTC
+  displayName: Weekly scheduled run
+  branches:
+    include: [main, maintenance/0.13.x]
+  always: true
 
 variables:
   MKL_NUM_THREADS: 1