/usr/share/ is a directory commonly accessed by various tools, hence we
really should make sure we umount it lazily (MNT_DETACH), since
otherwise there's a good chance that the umount might simply fail.
I noticed this there:
https://github.com/systemd/systemd/actions/runs/
21321690161/job/
61372465563?pr=40446
mountpoint /usr/share
touch /tmp/foo/abc
test -f /usr/share/abc
-umount /usr/share
+umount -l /usr/share
test ! -f /usr/share/abc
mount --bind /tmp/foo /usr/share
systemd-sysext unmerge
test ! -f /usr/lib/systemd/system/some_file
mountpoint /usr/share
-umount /usr/share
+umount -l /usr/share
rm -f /var/lib/extensions/app0.raw
exit 0