downgrade transformer 4.56.2

Signed-off-by: sirutBuasai <sirutbuasai27@outlook.com>

Author: sirutBuasai

.github/workflows/pr-vllm.yml

@@ -311,7 +311,7 @@ jobs:
             uv pip install --system pytest pytest-asyncio
             uv pip install --system -e tests/vllm_test_utils
             uv pip install --system hf_transfer
-            uv pip install --system transformers==4.57.3
+            uv pip install --system transformers==4.56.2
             mkdir src
             mv vllm src/vllm
           '
@@ -592,7 +592,7 @@ jobs:
             uv pip install --system pytest pytest-asyncio
             uv pip install --system -e tests/vllm_test_utils
             uv pip install --system hf_transfer
-            uv pip install --system transformers==4.57.3
+            uv pip install --system transformers==4.56.2
             mkdir src
             mv vllm src/vllm
           '
@@ -873,7 +873,7 @@ jobs:
             uv pip install --system pytest pytest-asyncio
             uv pip install --system -e tests/vllm_test_utils
             uv pip install --system hf_transfer
-            uv pip install --system transformers==4.57.3
+            uv pip install --system transformers==4.56.2
             mkdir src
             mv vllm src/vllm
           '