[submodule] Update submodule sonic-gnmi to the latest HEAD automatically (#19571)

#### Why I did it
src/sonic-gnmi
```
* 015de94 - (HEAD -> master, origin/master, origin/HEAD) Update gnmi-native to support subscribe stream mode (#271) (2 days ago) [ganglv]
* ccce9a2 - Return GNMI API error when ZMQ operation failed. (#270) (2 days ago) [Hua Liu]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld