Fix lint issue

Author: forman

zappend/config/config.py

@@ -120,7 +120,7 @@ def slice_engine(self) -> str | None:
         return self._config.get("slice_engine")
 
     @property
-    def slice_source(self) -> Callable[["Context", ...], "SliceSource"] | None:
+    def slice_source(self) -> Callable | None:
         """The configured slice source, if any."""
         return self._slice_source