Enabled the following tests on nrf54l20 - i2c_slave - clock_control_api - nrf_clock_calibration - nrf_lf_clock_start - onoff - retained_mem/api - uart_elementary - uart_errors - uart_mix_fifo_poll - uart_pm - uart_async_api - wdt_error_cases - wdt_basic_api - counter_basic_api - fcb - nrf/qdec Signed-off-by: Rafał Kuźnia <rafal.kuznia@nordicsemi.no>