[submodule] Update submodule sonic-gnmi to the latest HEAD automatically (sonic-net#21639)

#### Why I did it
src/sonic-gnmi
```
* f8c2979 - (HEAD -> master, origin/master, origin/HEAD) Remove the dependency on Jipanyang's personal repository (sonic-net#345) (23 hours ago) [ganglv]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld