fix unnecessary dict

Author: hoheinzollern

src/wagtailmarkdown/utils.py

@@ -34,9 +34,9 @@ def _transform_markdown_into_html(text):
 def _sanitise_markdown_html(markdown_html):
     nh3_kwargs = _get_nh3_kwargs()
     nh3_kwargs["tags"] = set(nh3_kwargs["tags"])
-    nh3_kwargs["attributes"] = {
-        key: set(value) for key, value in nh3_kwargs["attributes"].items()
-    }
+    nh3_kwargs["attributes"] = dict(
+        (key, set(value)) for key, value in nh3_kwargs["attributes"].items()
+    )
     nh3_kwargs["filter_style_properties"] = set(
         nh3_kwargs["filter_style_properties"]
     )