[CI] add weekly run

Author: jaapio

.github/workflows/integrate.yaml

@@ -7,6 +7,8 @@ on: # yamllint disable-line rule:truthy
     branches:
       - "5.x"
   pull_request: null
+  schedule:
+    - cron: '0 14 * * 1'
   # Allow manually triggering the workflow.
   workflow_dispatch: null