Update main.yml

.github/workflows/main.yml

@@ -6,11 +6,14 @@ on:
     paths-ignore:
       - '**.md'
       - '**.yml'
+      
+  # Note: This is different from "pull_request". Need to specify ref when doing checkouts.
   pull_request_target:
     branches: [ master ]
     paths-ignore:
       - '**.md'
       - '**.yml'
+
 jobs:
 
   ci-check:
@@ -21,6 +24,8 @@ jobs:
       uses: actions/checkout@v2
       with:
         submodules: 'recursive'
+        ref: ${{github.event.pull_request.head.ref}}
+        repository: ${{github.event.pull_request.head.repo.full_name}}
 
     - name: Install cppcheck
       run: |
@@ -60,6 +65,8 @@ jobs:
       uses: actions/checkout@v2
       with:
         submodules: 'recursive'
+        ref: ${{github.event.pull_request.head.ref}}
+        repository: ${{github.event.pull_request.head.repo.full_name}}
 
     - name: Setup Python
       uses: actions/setup-python@v2