change runs-on to a valid tag

.forgejo/workflows/demo.yaml

@@ -3,7 +3,7 @@ run-name: ${{ github.actor }} is testing
 on: [push]
 jobs:
   Explore-CI:
-    runs-on: ubuntu-latest
+    runs-on: self-hosted
     steps:
       - run: echo "The job was automatically triggered by a ${{ github.event_name }} event."
       - run: echo "This job is now running on a ${{ runner.os }} server."