Stop exiting early with `--fail-on-warnings; add --exception-on-warning` (#12743)

Co-authored-by: Jeremy Maitin-Shepard <jbms@google.com>

doc/usage/extensions/autodoc.rst

@@ -770,6 +770,10 @@ There are also config values that you can set:
    If ``False`` is given, autodoc forcedly suppresses the error if the imported
    module emits warnings.  By default, ``True``.
 
+   .. versionchanged:: 8.1
+      This option now has no effect as :option:`!--fail-on-warning`
+      no longer exits early.
+
 .. confval:: autodoc_inherit_docstrings
 
    This value controls the docstrings inheritance.