kn: enable checking out submodules recursively (#56)

Author: lauzadis

.github/actions/checkout-head/action.yml

@@ -62,4 +62,5 @@ runs:
         path: ${{ inputs.path }}
         repository: ${{ inputs.repository }}
         ref: ${{ steps.repo.outputs.ref }}
-        token: ${{ inputs.token }}
+        token: ${{ inputs.token }}
+        submodules: 'recursive'