[submodule] Update submodule sonic-gnmi to the latest HEAD automatically (#20515)

#### Why I did it
src/sonic-gnmi
```
* cb0a379 - (HEAD -> 202405, origin/202405) Update all the dbus timeout (#306) (26 hours ago) [ganglv]
* 81dbc3a - Use version of gocov supported by sonic-gnmi (#300) (2 days ago) [Zain Budhwani]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld