Update Doc/library/os.rst

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Author: vstinner

Doc/library/os.rst

@@ -219,7 +219,7 @@ process and user.
    :data:`os.environ`, and when one of the :meth:`~dict.pop` or
    :meth:`~dict.clear` methods is called.
 
-   If the ``clearenv()`` function is available, the :meth:`~dict.clear` method
+   If the :manpage:`clearenv(3)` function is available, the :meth:`~dict.clear` method
    uses it and emits a single ``os._clearenv`` audit event. Otherwise, it emits
    an ``os.unsetenv`` event on each deleted variable.