gitlab-ci: use "run-test-slice-meson.sh"

While our GitHub workflow already uses "ci/run-test-slice-meson.sh",
GitLab CI open-codes the parameters. Adapt the latter to also use the
same script so that we always use the same Meson options across both CI
systems.

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

.gitlab-ci.yml

@@ -183,7 +183,8 @@ test:msvc-meson:
     - job: "build:msvc-meson"
       artifacts: true
   script:
-    - meson test -C build --no-rebuild --print-errorlogs --slice $Env:CI_NODE_INDEX/$Env:CI_NODE_TOTAL
+    - |
+      & "C:/Program Files/Git/usr/bin/bash.exe" -l -c 'ci/run-test-slice-meson.sh build $CI_NODE_INDEX $CI_NODE_TOTAL'
   parallel: 10
   artifacts:
     reports: