github: hello_world_multiplatform: Adding rx-zephyr-elf

Adding rx-zephyr-elf for testing rx target

Signed-off-by: Duy Nguyen <duy.nguyen.xa@renesas.com>

Author: duynguyenxa

.github/workflows/hello_world_multiplatform.yaml

@@ -62,7 +62,7 @@ jobs:
         uses: zephyrproject-rtos/action-zephyr-setup@b2453c72966ee67b1433be22b250348d48283286 # v1.0.7
         with:
           app-path: zephyr
-          toolchains: aarch64-zephyr-elf:arc-zephyr-elf:arc64-zephyr-elf:arm-zephyr-eabi:mips-zephyr-elf:riscv64-zephyr-elf:sparc-zephyr-elf:x86_64-zephyr-elf:xtensa-dc233c_zephyr-elf:xtensa-sample_controller32_zephyr-elf
+          toolchains: aarch64-zephyr-elf:arc-zephyr-elf:arc64-zephyr-elf:arm-zephyr-eabi:mips-zephyr-elf:riscv64-zephyr-elf:sparc-zephyr-elf:x86_64-zephyr-elf:xtensa-dc233c_zephyr-elf:xtensa-sample_controller32_zephyr-elf:rx-zephyr-elf
 
       - name: Build firmware
         working-directory: zephyr