[CI/Build] Include Transformers backend test in nightly transformers test (vllm-project#25885)

Signed-off-by: Isotr0py <mozf@mail2.sysu.edu.cn>
Signed-off-by: Tomer Asida <57313761+tomeras91@users.noreply.github.com>

Author: Isotr0py

.buildkite/test-pipeline.yaml

@@ -752,6 +752,7 @@ steps:
   commands:
     - pip install --upgrade git+https://github.com/huggingface/transformers
     - pytest -v -s tests/models/test_initialization.py
+    - pytest -v -s tests/models/test_transformers.py
     - pytest -v -s tests/models/multimodal/processing/
     - pytest -v -s tests/models/multimodal/test_mapping.py
     - python3 examples/offline_inference/basic/chat.py