Correct the type hint on metadata()

Author: oschwald

HISTORY.rst

@@ -9,7 +9,9 @@ History
 * The type hints for the database file in the ``Reader`` constructor have
   been expanded to match those specified by ``maxmindb.open_database``. In
   particular, ``os.PathLike`` and ``IO`` have been added.
-
+* Corrected the type hint for the ``metadata()`` method on ``Reader``. It
+  will return a ``maxminddb.extension.Metadata`` if the C extension is being
+  used.
 
 4.2.0 (2021-05-12)
 ++++++++++++++++++

geoip2/database.py

@@ -258,7 +258,9 @@ def _flat_model_for(
         record["prefix_len"] = prefix_len
         return model_class(record)
 
-    def metadata(self) -> maxminddb.reader.Metadata:
+    def metadata(
+        self,
+    ) -> Union[maxminddb.reader.Metadata, "maxminddb.extension.Metadata"]:
         """The metadata for the open database.
 
         :returns: :py:class:`maxminddb.reader.Metadata` object