fix: include submodules

Author: maxrjones

.github/workflows/downstream.yml

@@ -73,6 +73,7 @@ jobs:
           repository: zarr-developers/numcodecs
           fetch-depth: 0
           path: numcodecs
+          submodules: recursive
           persist-credentials: false
 
       - uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0