fix: scheduler shutdown

[polBachelin]

Description

This PR is a fix for the issue : #1235

How Has This Been Tested?

• Running server locally with command : `python dbgpt/app/dbgpt_server.py
• Shutting down server with Ctrl + C

Snapshots:

Include snapshots for easier review.

Checklist:

• My code follows the style guidelines of this project
• I have already rebased the commits and make the commit message conform to the project standard.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged and published in downstream modules

[csunny]

@polBachelin Thanks for your PR， we fill make a test and merge.

[csunny]

Thanks, LGTM~

[fangyinc]

LGTM.