[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

nbconvert/filters/markdown_mistune.py

@@ -57,6 +57,7 @@ def import_plugin(name: str) -> "MarkdownPlugin":  # type: ignore[misc]
     try:
         from mistune.plugins import Plugin
     except ImportError:
+
         class Plugin(Protocol):
             def __call__(self, markdown: "Markdown") -> None: ...