[submodule] Update submodule linkmgrd to the latest HEAD automatically (

sonic-net#19844)

#### Why I did it
src/linkmgrd
```
* 287dbd7 - (HEAD -> master, origin/master, origin/HEAD) [link prober] print out error code message when `sendHeartbeat` fails (sonic-net#266) (34 hours ago) [Jing Zhang]
* 22f55a7 - Fix state machine handler race conditions introduced by `strand::wrap` (sonic-net#257) (9 days ago) [Longxiang Lyu]
```
#### How I did it
#### How to verify it
#### Description for the changelog