[submodule] Update submodule sonic-gnmi to the latest HEAD automatically (sonic-net#20675)

#### Why I did it
src/sonic-gnmi
```
* e844925 - (HEAD -> master, origin/master, origin/HEAD) Add support for RebootMethod_HALT for Reboot API (sonic-net#286) (28 hours ago) [Vasundhara Volam]
* e5125cb - Merge pull request sonic-net#316 from hdwhdw/ignore (31 hours ago) [Dawei Huang]
* c702d31 - Add build artifacts to gitignore. (2 days ago) [Dawei Huang]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld