Fix doc reference to decorator

Co-authored-by: Adam Turner <[email protected]>

Author: srittau

Doc/library/io.rst

@@ -1152,7 +1152,7 @@ Static Typing
 
 The following protocols can be used for annotating function and method
 arguments for simple stream reading or writing operations. They are decorated
-with :func:`@typing.runtime_checkable <typing.runtime_checkable>`.
+with :deco:`typing.runtime_checkable`.
 
 .. class:: Reader[T]