ci: Fix type of the fallback callable

Author: pawamoy

src/mkdocs_autorefs/plugin.py

@@ -57,7 +57,7 @@ def __init__(self) -> None:
         super().__init__()
         self._url_map: dict[str, str] = {}
         self._abs_url_map: dict[str, str] = {}
-        self.get_fallback_anchor: Callable[[str], str | None] | None = None
+        self.get_fallback_anchor: Callable[[str], tuple[str, ...]] | None = None
 
     def register_anchor(self, page: str, identifier: str) -> None:
         """Register that an anchor corresponding to an identifier was encountered when rendering the page.