ci: checkout@v2 supports submodules again

.github/workflows/assets.yml

@@ -21,13 +21,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-    - name: Checkout submodules
-      shell: bash
-      run: |
-        auth_header="$(git config --local --get http.https://github.com/.extraheader)"
-        git submodule sync --recursive
-        git -c "http.extraheader=$auth_header" -c protocol.version=2 submodule update --init --force --recursive --depth=1
-        git submodule absorbgitdirs
+      with:
+        submodules: recursive
+    - run: git submodule absorbgitdirs
     - run: |
         mkdir -p ~/.ssh
         echo "${{ secrets.id_rsa_ab }}" > ~/.ssh/id_rsa