[submodule] Update submodule sonic-gnmi to the latest HEAD automatically (#16833)

#### Why I did it
src/sonic-gnmi
```
* 8e13400 - (HEAD -> master, origin/master, origin/HEAD) Fix random build failures due to sonic_internal.proto (#157) (3 days ago) [Sachin Holla]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld