Add access token to SITL test Github Action

This is needed for downstream adopters. We want them to re-use our CI tests so that contributions already are pre-tested when they are submitted.

.github/workflows/sitl_tests.yml

@@ -8,6 +8,9 @@ jobs:
     container: px4io/px4-dev-simulation-bionic:2019-12-18
     steps:
     - uses: actions/checkout@v1
+      with:
+        token: ${{ secrets.ACCESS_TOKEN }}
+        submodules: true
     - name: Set Python 3 as default
       run: update-alternatives --install /usr/bin/python python /usr/bin/python3 10
     - name: Install psutil