[submodule] Update submodule sonic-gnmi to the latest HEAD automatically (sonic-net#21713)

#### Why I did it
src/sonic-gnmi
```
* 450bcdd - (HEAD -> master, origin/master, origin/HEAD) GNOI Implementation of OS.Activate (sonic-net#351) (3 hours ago) [Dawei Huang]
* 795f7ea - Merge pull request sonic-net#172 from faraazbrcm/rpc_from_proto (5 hours ago) [anand-kumar-subramanian]
* 4b2144a - Merge branch 'master' into rpc_from_proto (2 days ago) [Mohammed Faraaz]
* 913c789 - Support for YANG RPCs (11 months ago) [Mohammed Faraaz]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld