cargo-bazel: add libz as buildInput for darwin

Add libz as build input to allow building cargo-bazel on darwin.

pkgs/by-name/ca/cargo-bazel/package.nix

···
 {
   lib,
+  stdenv,
   fetchCrate,
   rustPlatform,
+  libz,
 }:
 
 rustPlatform.buildRustPackage rec {
···
     inherit pname version;
     hash = "sha256-FS1WFlK0YNq1QCi3S3f5tMN+Bdcfx2dxhDKRLXLcios=";
   };
+
+  buildInputs = lib.optional stdenv.isDarwin libz;
 
   useFetchCargoVendor = true;
   cargoHash = "sha256-E/yF42Vx9tv8Ik1j23El3+fI19ZGzq6nikVMATY7m3E=";