[ROCm][CI] Shard MI300 Multimodal Processor (#57056)

Signed-off-by: aarushjain29 <Aarushi.Jain2@amd.com>
Co-authored-by: Andreas Karatzas <akaratza@amd.com>

.buildkite/test-amd.yaml

@@ -2175,19 +2175,20 @@ steps:
   - pytest -v -s models/multimodal/generation/test_memory_leak.py -m core_model
   - cd .. && VLLM_WORKER_MULTIPROC_METHOD=spawn pytest -v -s tests/models/multimodal/generation/test_whisper.py -m core_model
 
-- label: ":amd: (MI300) Multimodal Processor" # 1h 42m
+- label: ":amd: (MI300) Multimodal Processor Shard %N" # TBD
   timeout_in_minutes: 110
   mirror_hardwares: [amdexperimental, amdproduction, amdgfx942nightly, amdmi300]
   dind: false
   agent_pool: mi300_1
   optional: true
+  parallelism: 4
   working_dir: "/vllm-workspace/tests"
   source_file_dependencies:
   - vllm/
   - tests/models/multimodal
   - tests/models/registry.py
   commands:
-  - pytest -v -s models/multimodal/processing/test_tensor_schema.py
+  - pytest -v -s models/multimodal/processing/test_tensor_schema.py --num-shards=$$BUILDKITE_PARALLEL_JOB_COUNT --shard-id=$$BUILDKITE_PARALLEL_JOB
 
 - label: ":amd: (MI300) Multimodal Models (Extended Pooling)" # TBD
   timeout_in_minutes: 75