[submodule] Update submodule sonic-platform-common to the latest HEAD automatically (sonic-net#20121)

#### Why I did it
src/sonic-platform-common
```
* 309a5fb - (HEAD -> master, origin/master, origin/HEAD) Make is_flat_memory more robust (sonic-net#491) (18 hours ago) [Junchao-Mellanox]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld