Tests fail with Mercurial 5.7rc0

Job #157184 failed for 2e9478f62ea3:

I posted a patch — https://foss.heptapod.net/octobus/mercurial-devel/-/commit/1d06709aa54a3eb92836c47fc7f260b44c125784 — against Mercurial that broke our test suite, intentionally:

changeset:   46479:72007a9ac064
user:        Dan Villiom Podlaski Christiansen <danchr@gmail.com>
date:        Sun Dec 20 15:38:50 2020 +0100
files:       mercurial/hg.py
description:
clone: update to active bookmark, if set

This cannot happen during a normal Mercurial clone, but is useful for extensions
like hg-git where we know what to check out — the Git HEAD — but do not wish to
track it later on using the `@` bookmark.

Test Plan:
I have not included an explicit test, as this is much more easily tested within
the `hg-git` test suite.

Differential Revision: https://phab.mercurial-scm.org/D9638