[submodule] Update submodule sonic-stp to the latest HEAD automatically (sonic-net#25460)

#### Why I did it
src/sonic-stp
```
* 586d842 - (HEAD -> master, origin/master, origin/HEAD) Merge pull request #85 from rustiqly/add-copilot-instructions (28 hours ago) [Lihua Yuan]
* 7db90db - Add .github/copilot-instructions.md for AI-assisted development (2 days ago) [Rustiqly]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld