Fix debug option in autosectionlabel documentation (#12324)

Co-authored-by: Françoise Conil <[email protected]>

Author: fconil

doc/usage/extensions/autosectionlabel.rst

@@ -51,6 +51,6 @@ Debugging
 ---------
 
 The ``WARNING: undefined label`` indicates that your reference in
-:rst:role:`ref` is mis-spelled. Invoking :program:`sphinx-build` with ``-vv``
+:rst:role:`ref` is mis-spelled. Invoking :program:`sphinx-build` with ``-vvv``
 (see :option:`-v`) will print all section names and the labels that have been
 generated for them. This output can help finding the right reference label.