Doc fix: the text role is called "func", not "funk".

Doc/library/os.rst

@@ -2225,7 +2225,7 @@ features:
 
    This function always supports :ref:`paths relative to directory descriptors
    <dir_fd>` and :ref:`not following symlinks <follow_symlinks>`.  Note however
-   that, unlike other functions, the :funk:`fwalk` default value for
+   that, unlike other functions, the :func:`fwalk` default value for
    *follow_symlinks* is ``False``.
 
    .. note::