Building html documentation fails on macOS for Sage 9.2.beta8.

Initial report:

• sage-release, 2020-08-13

Depends on #29552

CC: @jhpalmieri @slel @embray @kiwifb @kwankyu @tscrim @fchapoton @vbraun

Component: build

Author: Dima Pasechnik

Branch/Commit: 4b11a70

Reviewer: John Palmieri

Issue created by migration from https://trac.sagemath.org/ticket/30351