swiftpm2nix: fix hash mismatch when git submodules exist

pkgs/development/tools/swiftpm2nix/support.nix

···
         url = dep.packageRef.location;
         rev = dep.state.checkoutState.revision;
         sha256 = hashes.${dep.subpath};
+        fetchSubmodules = true;
       })) workspaceState.object.dependencies
     );
 

pkgs/development/tools/swiftpm2nix/swiftpm2nix.sh

···
 jq -r '.object.dependencies[] | "\(.subpath) \(.packageRef.location) \(.state.checkoutState.revision)"' $stateFile \
 | while read -r name url rev; do
   echo >&2 "-- Fetching $name"
-  sha256="$(nix-prefetch-git $url $rev | jq -r .sha256)"
+  sha256="$(nix-prefetch-git --fetch-submodules $url $rev | jq -r .sha256)"
   hashes+="
     \"$name\" = \"$sha256\";"
   echo >&2