fix(ci): wrap pod_spec GPU patch in spec.containers (Pod-level patch)

Strategic merge patches are applied to the Pod object, not PodSpec.
The patch needs {"spec":{"containers":[...]}} not {"containers":[...]}.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infra/k8s/gitlab/runner-values.yaml

@@ -48,7 +48,7 @@ runners:
       [[runners.kubernetes.pod_spec]]
         name = "build"
         patch_type = "strategic"
-        patch = '{"containers":[{"name":"build","resources":{"limits":{"nvidia.com/gpu":"1"},"requests":{"nvidia.com/gpu":"1"}}}]}'
+        patch = '{"spec":{"containers":[{"name":"build","resources":{"limits":{"nvidia.com/gpu":"1"},"requests":{"nvidia.com/gpu":"1"}}}]}}'
 
   # Runner tags for job matching
   tags: "kapsule,rust,docker,gpu"