fixup! wrap GeneratorModel methods into BoundMethod; remove redundant test

Author: temyurchenko

astroid/bases.py

@@ -718,6 +718,14 @@ def __str__(self) -> str:
 class AsyncGenerator(Generator):
     """Special node representing an async generator."""
 
+    def __init__(
+        self,
+        parent: nodes.FunctionDef,
+        generator_initial_context: InferenceContext | None = None,
+    ) -> None:
+        super().__init__(parent, generator_initial_context)
+        AsyncGenerator.special_attributes = objectmodel.AsyncGeneratorModel()
+
     def pytype(self) -> Literal["builtins.async_generator"]:
         return "builtins.async_generator"