0.16.0 docker not released yet

Signed-off-by: Taichang Zhou <tzhouam@connect.ust.hk>

docker/Dockerfile.ci

@@ -1,5 +1,5 @@
 ARG VLLM_BASE_IMAGE=vllm/vllm-openai
-ARG VLLM_BASE_TAG=v0.16.0
+ARG VLLM_BASE_TAG=v0.15.0
 FROM ${VLLM_BASE_IMAGE}:${VLLM_BASE_TAG}
 ARG APP_DIR=/workspace/vllm-omni
 WORKDIR ${APP_DIR}