[submodule] Update submodule sonic-snmpagent to the latest HEAD automatically (#17711)

#### Why I did it
src/sonic-snmpagent
```
* 29481f9 - (HEAD -> master, origin/master, origin/HEAD) Fix SNMP dropping some of the queue counter when create_only_config_db_buffers is set to true (#303) (69 minutes ago) [DavidZagury]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld