[sonic-platform-daemons] Update submodule (#6535)

Submodule changes to be committed:

* src/sonic-platform-daemons 81318f7...e72f6cd (3):
  > [ledd] Minor refactor; add unit tests (#143)
  > [thermalctld] Report unit test coverage (#141)
  > [psud] Increase unit test coverage (#140)