[submodule] Update submodule sonic-gnmi to the latest HEAD automatically (#20013)

#### Why I did it
src/sonic-gnmi
```
* 9705bed - (HEAD -> 202405, origin/202405) Use server GracefulStop instead of force stop (#219) (27 hours ago) [Zain Budhwani]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld