bpo-37116: Use PEP 570 syntax for positional-only parameters. (GH-13700)

diff --git a/Doc/library/weakref.rst b/Doc/library/weakref.rst
index 80a908b..a28d710 100644
--- a/Doc/library/weakref.rst
+++ b/Doc/library/weakref.rst
@@ -396,7 +396,7 @@
    import weakref
 
    class ExtendedRef(weakref.ref):
-       def __init__(self, ob, callback=None, **annotations):
+       def __init__(self, ob, callback=None, /, **annotations):
            super(ExtendedRef, self).__init__(ob, callback)
            self.__counter = 0
            for k, v in annotations.items():