GHA: update forward action

Author: junghans

.github/workflows/forward-to-votca.yml

@@ -10,9 +10,14 @@ jobs:
     if: github.repository_owner == 'votca'
     runs-on: ubuntu-latest
     steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+        with:
+          repository: votca/votca
+          ref: master
+          fetch-depth: 0
+          token: ${{ secrets.VOTCA_BOT_TOKEN }}
       - name: Update submodule
         uses: votca/actions/forward@master
         with:
           module: ${{ github.repository }}
-          token: ${{ secrets.VOTCA_BOT_TOKEN }}
-