fix dp_rank env

[ByronHsu]

Motivation

Fix the issue

  File "/home/jobuser/resources/sglang/python/sglang/srt/managers/scheduler.py", line 1392, in run_scheduler_process
    dp_rank = int(os["DP_RANK"])
TypeError: 'module' object is not subscriptable

Modifications

Checklist

• Format your code according to the Contributor Guide.
• Add unit tests as outlined in the Contributor Guide.
• Update documentation as needed, including docstrings or example tutorials.