[submodule] Update submodule sonic-snmpagent to the latest HEAD automatically (#24644)

#### Why I did it
src/sonic-snmpagent
```
* 6dac47c - (HEAD -> master, origin/master, origin/HEAD) Migrate agent pool from ubuntu-20.04 to ubuntu-latest (#362) (28 minutes ago) [yijingyan2]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld