[Doc] Add USE_MODELSCOPE_HUB=0 to lm-eval guide (#7279)

## Summary
- Add `USE_MODELSCOPE_HUB=0` to both Online and Offline lm-eval sections
- Add explanatory notes about Docker containers launching with
`VLLM_USE_MODELSCOPE=True`

The Docker containers set `VLLM_USE_MODELSCOPE=True`, which causes
lm-eval to download datasets from ModelScope instead of HuggingFace,
resulting in "Repo not exists" errors. Setting `USE_MODELSCOPE_HUB=0`
disables this behavior.

Fixes #607
- vLLM version: v0.17.0
- vLLM main:
4034c3d32e

Signed-off-by: bazingazhou233-hub <bazingazhou233-hub@users.noreply.github.com>
Co-authored-by: bazingazhou233-hub <bazingazhou233-hub@users.noreply.github.com>

docs/source/developer_guide/evaluation/using_lm_eval.md

@@ -106,9 +106,17 @@ Install lm-eval in the container:
 
 ```bash
 export HF_ENDPOINT="https://hf-mirror.com"
+export USE_MODELSCOPE_HUB=0
 pip install lm-eval[api]
 ```
 
+:::{note}
+The Docker container is launched with `VLLM_USE_MODELSCOPE=True`, which may
+cause lm-eval to download datasets from ModelScope instead of HuggingFace.
+Setting `USE_MODELSCOPE_HUB=0` disables this behavior so that lm-eval can
+fetch datasets from HuggingFace correctly.
+:::
+
 Run the following command:
 
 ```shell
@@ -170,9 +178,17 @@ Install lm-eval in the container:
 
 ```bash
 export HF_ENDPOINT="https://hf-mirror.com"
+export USE_MODELSCOPE_HUB=0
 pip install lm-eval
 ```
 
+:::{note}
+The Docker container is launched with `VLLM_USE_MODELSCOPE=True`, which may
+cause lm-eval to download datasets from ModelScope instead of HuggingFace.
+Setting `USE_MODELSCOPE_HUB=0` disables this behavior so that lm-eval can
+fetch datasets from HuggingFace correctly.
+:::
+
 Run the following command:
 
 ```shell