CI: Fix error when running on host-arm64

When pulling a base image from Docker Hub, the architecture
defaults to that of the native host, which is typically x86_64
or amd64 on GitHub runners. Since the run-on-arch-action
GitHub Action aims to run rv32emu on an ARM64 Ubuntu image, it
attempts to pull the native host manifest (either x86_64 or
amd64), resulting in a 'no match for platform in manifest'
error unless the --platform option is specified. Therefore,
specifying the --platform option as linux/arm64 resolves this
issue.

Close sysprog21#502

Author: ChinYikMing

.github/workflows/main.yml

@@ -94,8 +94,9 @@ jobs:
       # https://github.com/uraimo/run-on-arch-action
       uses: uraimo/run-on-arch-action@v2
       with:
-        arch: aarch64
-        distro: ubuntu22.04
+        arch: none
+        distro: none
+        base_image: "--platform=linux/arm64 arm64v8/ubuntu:22.04"
         # No 'sudo' is available
         install: |
           apt-get update -q -y