tests: drivers: watchdog: wdt_basic_api: Enable test on nRF54L09 and L20

Enable wdt_basic_api test on:
- nrf54l09pdk/nrf54l09/cpuapp (missing supported),
- nrf54l09pdk/nrf54l09/cpuflpr (missing overlay),
- nrf54l20pdk/nrf54l20/cpuflpr (missing supported and overlay).

Signed-off-by: Sebastian Głąb <sebastian.glab@nordicsemi.no>