Add private action to allow for testing

.github/workflows/main.yml

@@ -0,0 +1,15 @@
+name: Test
+
+on:
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Test talisman
+        uses: ./
+        with:
+          args: refs/heads/main ${{ github.event.after }} refs/heads/main ${{ github.event.before }}