need recursive submodules

Author: fbergmann

.github/workflows/experimental_wheels.yml

@@ -16,7 +16,7 @@ jobs:
     - uses: actions/checkout@v2
       with:
         fetch-depth: 0  # Optional, use if you use setuptools_scm
-        submodules: true  # Optional, use if you have submodules
+        submodules: recursive  # Optional, use if you have submodules
 
     - name: Build SDist
       run: pipx run build --sdist
@@ -38,7 +38,7 @@ jobs:
     steps:
     - uses: actions/checkout@v1
       with:
-        submodules: true
+        submodules: recursive
 
     - uses: pypa/cibuildwheel@v2.3.1
       env: