[submodule] Update submodule sonic-swss to the latest HEAD automatically (sonic-net#20159)

#### Why I did it
src/sonic-swss
```
* 20e8b362 - (HEAD -> master, origin/master, origin/HEAD) [dash] Set CA to PA underlay DIP for static encap (sonic-net#3286) (5 days ago) [Lawrence Lee]
* 60f9dde5 - Add pass pl_sip_encoding to SAI (sonic-net#3285) (5 days ago) [Lawrence Lee]
* 3943093d - [Mellanox] Update headroom calculation algorithm (sonic-net#3235) (6 days ago) [Stephen Sun]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld