actions/example-pull-request: checkout gets the default branch

actions/example-pull-request/.forgejo/workflows/test.yml

@@ -9,7 +9,7 @@ jobs:
   test:
     runs-on: docker
     container:
-      image: code.forgejo.org/oci/debian:bookworm
+      image: code.forgejo.org/oci/node:20-bookworm
       options: "--volume /srv/example-pull-request:/srv/example-pull-request"
 
     steps:
@@ -120,3 +120,20 @@ jobs:
           cat > $d/event <<'EOF'
           ${{ toJSON(github.event) }}
           EOF
+
+      - uses: https://code.forgejo.org/actions/checkout@v4
+      - name: checkout the default branch if pull_request_target
+        run: |
+          set -x
+          case $GITHUB_EVENT_NAME in
+            pull_request_target)
+              ! test -f file-unique-to-the-pr-branch
+              ;;
+            pull_request)
+              test -f file-unique-to-the-pr-branch
+              ;;
+            *)
+              echo unexpected event $GITHUB_EVENT_NAME
+              false
+              ;;
+          esac