bpo-39231: correct tutorial annotations section (GH-25029)

Author: iritkatriel

Doc/tutorial/controlflow.rst

@@ -1038,7 +1038,7 @@ function.  Parameter annotations are defined by a colon after the parameter name
 by an expression evaluating to the value of the annotation.  Return annotations are
 defined by a literal ``->``, followed by an expression, between the parameter
 list and the colon denoting the end of the :keyword:`def` statement.  The
-following example has a positional argument, a keyword argument, and the return
+following example has a required argument, an optional argument, and the return
 value annotated::
 
    >>> def f(ham: str, eggs: str = 'eggs') -> str: