ci/lib: fix "CI setup" sections with GitLab CI

ci/lib: fix "CI setup" sections with GitLab CI

Whenever we source "ci/lib.sh" we wrap the directives in a separate
group so that they can easily be collapsed in the web UI. And as we
source the script multiple times during a single CI run we thus end up
with the same section name reused multiple times, as well.

This is broken on GitLab CI though, where reusing the same group name is
not supported. The consequence is that only the last of these sections
can be collapsed.

Fix this issue by including the name of the sourcing script in the
group's name.

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