do nothing if nothing is pushed

Fixes: https://code.forgejo.org/actions/cascading-pr/issues/6

tests/originrepo-do-nothing/.forgejo/workflows/test.yml

@@ -0,0 +1,25 @@
+# SPDX-License-Identifier: MIT
+name: test
+on:
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - closed
+jobs:
+  test:
+    runs-on: docker
+    steps:
+      - uses: actions/checkout@v4
+      - uses: SELF@vTest
+        with:
+          origin-url: ${{ env.GITHUB_SERVER_URL }}
+          origin-repo: user1/originrepo-do-nothing
+          origin-token: ${{ secrets.ORIGIN_TOKEN }}
+          origin-pr: ${{ github.event.pull_request.number }}
+          destination-url: ${{ env.GITHUB_SERVER_URL }}
+          destination-repo: user2/destinationrepo
+          destination-branch: main
+          destination-token: ${{ secrets.DESTINATION_TOKEN }}
+          update: /bin/true
+          debug: true

tests/originrepo-do-nothing/README

@@ -0,0 +1 @@
+originrepo