gh-114384: Align sys.set_asyncgen_hooks signature in docs to reflect implementation (#114385)

Author: sobolevn

Doc/library/sys.rst

@@ -1655,7 +1655,7 @@ always available.
       ``'opcode'`` event type added; :attr:`~frame.f_trace_lines` and
       :attr:`~frame.f_trace_opcodes` attributes added to frames
 
-.. function:: set_asyncgen_hooks(firstiter, finalizer)
+.. function:: set_asyncgen_hooks([firstiter] [, finalizer])
 
    Accepts two optional keyword arguments which are callables that accept an
    :term:`asynchronous generator iterator` as an argument. The *firstiter*

Python/sysmodule.c

@@ -1420,7 +1420,7 @@ sys_set_asyncgen_hooks(PyObject *self, PyObject *args, PyObject *kw)
 }
 
 PyDoc_STRVAR(set_asyncgen_hooks_doc,
-"set_asyncgen_hooks(* [, firstiter] [, finalizer])\n\
+"set_asyncgen_hooks([firstiter] [, finalizer])\n\
 \n\
 Set a finalizer for async generators objects."
 );