[GR-61695] Fix and improve GHA gate.

PullRequest: graal/19926

Author: fniephaus

.github/workflows/main.yml

@@ -57,6 +57,8 @@ on:
       - '**.md'
       - '**.jsonnet'
       - '**.libjsonnet'
+  schedule:
+  - cron: '30 0 * * 1'
   # Enable manual dispatch of the workflow
   # see https://docs.github.com/en/actions/managing-workflow-runs/manually-running-a-workflow
   workflow_dispatch:
@@ -231,6 +233,7 @@ jobs:
     timeout-minutes: 60
     env:
       MX_PYTHON: 'python'
+      PYTHONIOENCODING: 'utf-8'
     steps:
     - name: Checkout oracle/graal
       uses: actions/checkout@v4