add schedule runs-on variables test for post 7.0 releases (#151)

reimplements: forgejo/end-to-end#146 for 8.0-dev and 8.0-test
Reviewed-on: https://code.forgejo.org/forgejo/end-to-end/pulls/151
Reviewed-by: earl-warren <earl-warren@noreply.code.forgejo.org>
Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-committed-by: TheFox0x7 <thefox0x7@gmail.com>

actions/example-post-7-0-schedule/.forgejo/workflows/test.yml

@@ -0,0 +1,23 @@
+on:
+  schedule:
+    - cron: '* * * * *'
+
+jobs:
+  test:
+    runs-on: ${{ vars.TEST_SCHEDULE_RUNSON }}
+    container:
+      image: code.forgejo.org/oci/debian:bookworm
+      options: "--volume /srv/example:/srv/example"
+
+    steps:
+      - run: |
+          echo "TEST_SCHEDULE_RUNSON=${{ vars.TEST_SCHEDULE_RUNSON }}"
+          touch /srv/example/post-7-0-schedule-volume/DONE
+
+      - name: save context
+        run: |
+          d=/srv/example/post-7-0-schedule/contexts/$GITHUB_EVENT_NAME
+          mkdir -p $d
+          cat > $d/github <<'EOF'
+          ${{ toJSON(github) }}
+          EOF