tests: drivers: uart: Add overlay for mcb_rx26t async test

Add overlay for mcb_rx26t uart async test

Signed-off-by: Quy Tran <[email protected]>

Author: quytranpzz

tests/drivers/uart/uart_async_api/boards/mcb_rx26t.overlay

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2025 Renesas Electronics Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&pinctrl {
+	sci5_default: sci5_default {
+		group1 {
+			psels = <RX_PSEL(RX_PSEL_PAnPFS_TXD5, 9, 0)>,
+			<RX_PSEL(RX_PSEL_PAnPFS_RXD5, 14, 0)>;
+		};
+	};
+};
+
+&sci5 {
+	pinctrl-0 = <&sci5_default>;
+	pinctrl-names = "default";
+	status = "okay";
+
+	dut: uart {
+		current-speed = <115200>;
+		status = "okay";
+	};
+};