tests: uart: update overlay for RA8x1

Add interrupts information for these boards:
- ek_ra8d1
- mck_ra8t1

Signed-off-by: The Nguyen <the.nguyen.yf@renesas.com>

Author: thenguyenyf

tests/drivers/uart/uart_async_api/boards/ek_ra8d1.overlay

@@ -20,6 +20,8 @@
 &sci2 {
 	pinctrl-0 = <&sci2_default>;
 	pinctrl-names = "default";
+	interrupts = <92 12>, <93 12>, <94 12>, <95 12>;
+	interrupt-names = "rxi", "txi", "tei", "eri";
 	status = "okay";
 	dut: uart {
 		current-speed = <115200>;

tests/drivers/uart/uart_async_api/boards/mck_ra8t1.overlay

@@ -20,6 +20,8 @@
 &sci4 {
 	pinctrl-0 = <&sci4_default>;
 	pinctrl-names = "default";
+	interrupts = <92 12>, <93 12>, <94 12>, <95 12>;
+	interrupt-names = "rxi", "txi", "tei", "eri";
 	status = "okay";
 	dut: uart {
 		current-speed = <115200>;