ci: Skip check-only container jobs for pre-merge

For pre-merge pipelines, we know that we don't need to run the
container-check jobs unless image-tags.yml has been modified. In this
case, we can just skip the container jobs, because we 'know' that the
containers are present in the upstream repo.

For downstream or off-main pipelines, we still need to run the check
job, because the changed-file tracking is not reliable on other
branches, and because we may need to copy the container image from the
upstream container storage into the user's namespace.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35203>

src/microsoft/ci/gitlab-ci.yml

@@ -10,8 +10,9 @@ test-spirv2dxil-windows:
   dependencies:
     - windows-msvc
   needs:
-    - windows-msvc
-    - windows_test_msvc
+    - job: windows-msvc
+    - job: windows_test_msvc
+      optional: true
     - !reference [.required-for-hardware-jobs, needs]
   variables:
     GIT_STRATEGY: none # testing doesn't build anything from source
@@ -32,8 +33,9 @@ test-dozen-deqp:
   dependencies:
     - windows-msvc
   needs:
-    - windows-msvc
-    - windows_test_msvc
+    - job: windows-msvc
+    - job: windows_test_msvc
+      optional: true
     - !reference [.required-for-hardware-jobs, needs]
   variables:
     GIT_STRATEGY: none # testing doesn't build anything from source