tests: app_dev: ram_context_for_isr: fix irq_num

This commit fixes the type of `irq_num` in the `fake_driver_config`
structure to `uint16_t`. This is to match the expected type for the case
where  `TEST_IRQ_NUM = (CONFIG_NUM_IRQS - 1)`, on platforms with more
than 256 IRQs.

Signed-off-by: Youssef Zini <[email protected]>

Author: youssefz24

tests/application_development/ram_context_for_isr/include/fake_driver.h

@@ -34,7 +34,7 @@ typedef void (*fake_driver_irq_callback_t)(const struct device *dev, void *user_
 
 struct fake_driver_config {
 	void (*irq_config_func)(void);
-	uint8_t irq_num;
+	uint16_t irq_num;
 	uint8_t irq_priority;
 };