Because 3 x 3 = 9 and we are at 9.0.beta3 these are three reasons to do the switch... see

https://groups.google.com/forum/#!topic/sage-devel/fmQbbSctZ-I

Depends on #28657

CC: @sagetrac-tmonteil

Component: misc

Author: Frédéric Chapoton

Branch: 715e85a

Reviewer: John Palmieri, Eric Gourgoulhon

Issue created by migration from https://trac.sagemath.org/ticket/28660