[ci] Switch some CI jobs to H200 MIG slices (#38956)

.buildkite/test_areas/models_multimodal.yaml

@@ -4,6 +4,7 @@ depends_on:
 steps:
 - label: "Multi-Modal Models (Standard) 1: qwen2"
   timeout_in_minutes: 45
+  device: h200_18gb
   source_file_dependencies:
   - vllm/
   - tests/models/multimodal
@@ -19,6 +20,7 @@ steps:
 
 - label: "Multi-Modal Models (Standard) 2: qwen3 + gemma"
   timeout_in_minutes: 45
+  device: h200_18gb
   source_file_dependencies:
   - vllm/
   - tests/models/multimodal
@@ -77,6 +79,7 @@ steps:
 
 - label: Multi-Modal Processor # 44min
   timeout_in_minutes: 60
+  device: h200_18gb
   source_file_dependencies:
   - vllm/
   - tests/models/multimodal
@@ -131,6 +134,7 @@ steps:
 
 - label: Multi-Modal Models (Extended Pooling)
   optional: true
+  device: h200_18gb
   source_file_dependencies:
   - vllm/
   - tests/models/multimodal/pooling