tests: gpio: basic_api: correct constant test for interrupt trigger

Interrupts default to trigger on level for historical reasons, so use of
GPIO_INT_LEVEL` as a mask results in a zero value.  Use a mask macro to
isolate the trigger configuration.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>

tests/drivers/gpio/gpio_basic_api/src/test_callback_trigger.c

@@ -93,7 +93,7 @@ static int test_callback(int mode)
 		goto pass_exit;
 	}
 
-	if ((mode & GPIO_INT_LEVEL) == GPIO_INT_LEVEL) {
+	if ((mode & GPIO_INT_TRIGGER_MASK) == GPIO_INT_LEVEL) {
 		if (cb_cnt != MAX_INT_CNT) {
 			TC_ERROR("not trigger callback correctly\n");
 			goto err_exit;