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

…lly (sonic-net#16014)

#### Why I did it
src/sonic-gnmi
```
* 58a7b20 - (HEAD -> master, origin/master, origin/HEAD) Add delete field to On change response when key is deleted (sonic-net#139) (8 hours ago) [Zain Budhwani]
```
#### How I did it
#### How to verify it
#### Description for the changelog