[submodule] Update submodule sonic-snmpagent to the latest HEAD autom…

…atically (sonic-net#17863)

#### Why I did it
src/sonic-snmpagent
```
* 6f59d29 - (HEAD -> 202305, origin/202305) Fix SNMP dropping some of the queue counter when create_only_config_db_buffers is set to true (sonic-net#303) (sonic-net#309) (33 minutes ago) [mssonicbld]
```
#### How I did it
#### How to verify it
#### Description for the changelog