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

…lly (#20471)

#### Why I did it
src/sonic-gnmi
```
* 91c05b8 - (HEAD -> 202405, origin/202405) Increase dbus timeout for gcu (#292) (#294) (2 days ago) [mssonicbld]
* 309dc5b - [ci] Allow partially succeeded build when downloading. (#298) (2 days ago) [Liu Shilong]
```
#### How I did it
#### How to verify it
#### Description for the changelog