.github: allow dispatching version updates manually and run on predefined schedule

.github/workflows/versions.yaml

 name: Upgrade to latest versions
 
-on: workflow_dispatch
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '37 7 * * 1'
 jobs:
   versions:
     runs-on: ubuntu-latest
     strategy:
       matrix:
         branch:
-          - 'release-0.5'
-          - 'release-0.6'
           - 'release-0.7'
           - 'release-0.8'
           - 'main'