enable openai workflow on fork branch (#82)

* update

* update

* Update openai.yml

.github/workflows/openai.yml

@@ -4,7 +4,7 @@
 name: OpenAI
 
 on:
-  pull_request:
+  pull_request_target:
     branches: ['main']
     paths:
       - 'autogen/**'
@@ -25,7 +25,11 @@ jobs:
     runs-on: ${{ matrix.os }}
     environment: openai
     steps:
-      - uses: actions/checkout@v3
+      # checkout to pr branch
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v4
         with: