[Deps] Retire the CUDA 12 lane (#38404)

Co-authored-by: Mohammad Angkad <mohammad.angkad@radixark.ai>

docker/sgl-deep-gemm.Dockerfile

@@ -27,8 +27,7 @@ RUN --mount=type=cache,id=sgl-deep-gemm-pip,target=/root/.cache/pip \
     set -eux; \
     case "${CUDA_VERSION}" in \
       13.0) CU_TAG=cu130 ;; \
-      12.9) CU_TAG=cu129 ;; \
-      *)    CU_TAG=cu130 ;; \
+      *) echo "Unsupported CUDA version: ${CUDA_VERSION}" && exit 1 ;; \
     esac; \
     ${PYTHON_ROOT_PATH}/bin/pip install torch==${TORCH_VER} --index-url https://${PYTORCH_MIRROR}/whl/${CU_TAG}; \
     ${PYTHON_ROOT_PATH}/bin/pip install --index-url ${PIP_DEFAULT_INDEX} \