doc: fix bug report Github template formatting (vllm-project#17486)

Signed-off-by: David Xia <david@davidxia.com>

Author: davidxia

.github/ISSUE_TEMPLATE/400-bug-report.yml

@@ -21,12 +21,12 @@ body:
  It is suggested to download and execute the latest script, as vllm might frequently update the diagnosis information needed for accurately and quickly responding to issues.
  value: |
  <details>
- <summary>The output of `python collect_env.py`</summary>
+ <summary>The output of <code>python collect_env.py</code></summary>
 
  ```text
  Your output of `python collect_env.py` here
  ```
- 
+
  </details>
  validations:
  required: true