[Doc] Add qwen3 embedding 8b guide (#1734)

1. Add the tutorials for qwen3-embedding-8b
2. Remove VLLM_USE_V1=1  in docs, it's useless any more from 0.9.2


- vLLM version: v0.9.2
- vLLM main:
5923ab9524

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

docs/source/developer_guide/contribution/testing.md

@@ -156,7 +156,7 @@ There are several principles to follow when writing unit tests:
 ```bash
 # Run unit tests
 export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/Ascend/ascend-toolkit/latest/$(uname -m)-linux/devlib
-VLLM_USE_V1=1 TORCH_DEVICE_BACKEND_AUTOLOAD=0 pytest -sv tests/ut
+TORCH_DEVICE_BACKEND_AUTOLOAD=0 pytest -sv tests/ut
 ```
 
 ::::