samples: matter: added lock 21540ek on 52840 sample

Graviton added as integration platform to sample lock.debug.nrf21540ek

Signed-off-by: Hubert Górski <hubert.gorski@nordicsemi.no>

samples/matter/lock/sample.yaml

@@ -29,6 +29,7 @@ tests:
  build_only: true
  extra_args: SHIELD=nrf21540ek
  integration_platforms:
+ - nrf52840dk_nrf52840
  - nrf5340dk_nrf5340_cpuapp
  platform_allow: nrf52840dk_nrf52840 nrf5340dk_nrf5340_cpuapp
  sample.matter.lock.switchable_thread.nrf7002_ek: