Use ci_vllm_version when recording vLLM commit (#1689)

### What this PR does / why we need it?
Use ci_vllm_version when recording vllm commit

Followup on https://github.com/vllm-project/vllm-ascend/pull/1623

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
- Test mannually.
$ python3 docs/source/conf.py | jq .ci_vllm_version | tr -d '"'
v0.9.2
- Test on my local repo: https://github.com/Yikun/vllm-ascend/pull/35

- vLLM version: v0.9.1
- vLLM main:
49e8c7ea25

Signed-off-by: Yikun Jiang <yikunkero@gmail.com>

docs/source/conf.py

@@ -76,6 +76,8 @@ myst_substitutions = {
     'pip_vllm_version': "0.9.1",
     # CANN image tag
     'cann_image_tag': "8.1.rc1-910b-ubuntu22.04-py3.10",
+    # vllm version in ci
+    'ci_vllm_version': 'v0.9.2',
 }
 
 # Add any paths that contain templates here, relative to this directory.