[submodule] Update submodule sonic-gnmi to the latest HEAD automatica…

…lly (#15921)

#### Why I did it
src/sonic-gnmi
```
* 610509b - (HEAD -> master, origin/master, origin/HEAD) Install necessary debs instead of entire artifact in azp (#137) (2 hours ago) [Zain Budhwani]
```
#### How I did it
#### How to verify it
#### Description for the changelog