There are two possible issues, both of which emit very long messages
from git:
- when shallow cloning via depth + a pinned commit we locally init
rather than cloning; use an almost-certainly not conflicting dummy
branch name
- any time a checkout of a revision is performed, it might not be a
branch name, in which case it will be a detached HEAD. By default git
is very noisy about this -- it wants you to know what happened and how
not to mess up. But wraps aren't per default intended for user editing
and development, it's just part of the internal transport which meson
uses. So, temporarily squelch this advice. Do not permanently
configure the repo like this though, because the user *might* cd in
and start developing on the subproject; in this case, any additional
git advice they trigger is their responsibility (and they probably do
want it).
Fixes#9318
b57b1050a6