gitlab-ci: ignore failures to disable realtime monitoring

gitlab-ci: ignore failures to disable realtime monitoring

We have recently introduced a change to disable realtime monitoring for
Windows job in GitLab CI. This change led (and still leads) to a quite
significant speedup.

But there's a catch: seemingly, some of the runners we use already have
realtime monitoring disabled. On such a machine, trying to disable the
feature again leads to an error that causes the whole job to fail.

Safeguard against such failures by explicitly ignoring them.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>