fix: wheel directory check for notebook workflow (#3532)

Coerce types to check if wheels exist, then create the directory.

Fixes #3528

src/bentoml/_internal/bento/build_config.py

@@ -514,7 +514,7 @@ def write_to_bento(self, bento_fs: FS, build_ctx: str) -> None:
         build_bentoml_editable_wheel(bento_fs.getsyspath(wheels_folder))
 
         # Move over required wheel files
-        if self.wheels is not None:
+        if self.wheels:
             bento_fs.makedirs(wheels_folder, recreate=True)
             for whl_file in self.wheels:  # pylint: disable=not-an-iterable
                 whl_file = resolve_user_filepath(whl_file, build_ctx)