Because POSIX sh was, with hindsight, not a particularly well-designed
programming language, if we don't 'set -e', then we'll respond to failure
of a setup command such as cd by carrying on regardless.
Signed-off-by: Simon McVittie <smcv@debian.org>
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2009>