gitlab-ci: always run MSVC-based Meson job

gitlab-ci: always run MSVC-based Meson job

With 7304bd2bc39 (ci: wire up Visual Studio build with Meson,
2025-01-22) we have introduced a CI job that builds and tests Git with
Microsoft Visual Studio via Meson. This job is only being executed by
default on GitHub Workflows though -- on GitLab CI it is marked as a
"manual" job, so the developer has to actively trigger these jobs.

The consequence of this split is that any breakage specific to this job
is only noticed by developers who mainly work with GitHub. Let's improve
this situation by also running the job by default on GitLab CI.

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