Properly serialise css_files and script_files

Author: AA-Turner

sphinxcontrib/serializinghtml/__init__.py

@@ -63,6 +63,11 @@ def get_target_uri(self, docname: str, typ: str | None = None) -> str:
         return docname + SEP
 
     def dump_context(self, context: dict, filename: str | os.PathLike[str]) -> None:
+        context = context.copy()
+        if 'css_files' in context:
+            context['css_files'] = [css.filename for css in context['css_files']]
+        if 'script_files' in context:
+            context['script_files'] = [js.filename for js in context['script_files']]
         if self.implementation_dumps_unicode:
             with open(filename, 'w', encoding='utf-8') as ft:
                 self.implementation.dump(context, ft, *self.additional_dump_args)