[nrf fromlist] tests: drivers: adc_api: change second channel gain for nrf54.

Upstream PR: zephyrproject-rtos/zephyr#76088

It will increase test coverage for adc driver, no test uses
ADC_GAIN_2_3 setting yet.

Signed-off-by: Bartlomiej Buczek <[email protected]>
(cherry picked from commit 71ae6ff6f10497e816fcf2da05ee0887dd5452df)

Author: nordic-babu

tests/drivers/adc/adc_api/boards/nrf54h20dk_nrf54h20_cpuapp.overlay

@@ -34,7 +34,7 @@
 
 	channel@2 {
 		reg = <2>;
-		zephyr,gain = "ADC_GAIN_1_2";
+		zephyr,gain = "ADC_GAIN_2_3";
 		zephyr,reference = "ADC_REF_INTERNAL";
 		zephyr,acquisition-time = <ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 10)>;
 		zephyr,input-positive = <NRF_SAADC_AIN2>;

tests/drivers/adc/adc_api/boards/nrf54l15dk_nrf54l15_cpuapp.overlay

@@ -34,7 +34,7 @@
 
 	channel@2 {
 		reg = <2>;
-		zephyr,gain = "ADC_GAIN_2_5";
+		zephyr,gain = "ADC_GAIN_2_3";
 		zephyr,reference = "ADC_REF_INTERNAL";
 		zephyr,acquisition-time = <ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 10)>;
 		zephyr,input-positive = <NRF_SAADC_AIN2>;