gitlab: make check-[dco|patch] a little more verbose

gitlab: make check-[dco|patch] a little more verbose

When git fails the rather terse backtrace only indicates it failed
without some useful context. Add some to make the log a little more
useful.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20241023113406.1284676-11-alex.bennee@linaro.org>
(cherry picked from commit 97f116f9c6fd127b6ed2953993fa9fb05e82f450)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: context fix for stable-7.2)