fix: use get_origin() for typing.GenericAlias detection

Fixes #3745 by checking the origin of type expressions instead of
their class type. typing.Dict[str, Any] is a typing._GenericAlias,
not a types.GenericAlias, so the previous check failed to match it.

This ensures consistent behavior between typing.Dict and dict annotations,
preventing silent schema changes when Ruff UP006 rewrites old-style
annotations to modern syntax.

Author: Jihaochang1

src/mcp/server/mcpserver/utilities/func_metadata.py

@@ -500,7 +500,7 @@ def _create_output_model(original_annotation: Any, type_expr: Any, func_name: st
         wrap_output = True
 
     # Handle GenericAlias types (list[str], dict[str, int], Union[str, int], etc.)
-    elif isinstance(type_expr, GenericAlias):
+    elif get_origin(type_expr) is not None:
         origin = get_origin(type_expr)
 
         if origin is dict: