Also test arm runner for building docker image

Author: hsbt

.github/workflows/test.yml

@@ -8,7 +8,7 @@ on:
 jobs:
   build:
     name: ${{ matrix.ruby_version }}-${{ matrix.ubuntu_version }}
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.arch == 'arm64' && 'ubuntu-24.04-arm' || 'ubuntu-24.04' }}
     strategy:
       matrix:
         ubuntu_version:
@@ -19,13 +19,16 @@ jobs:
           - 3.1.6
           - 3.2.4
           - 3.3.3
+        arch:
+          - amd64
+          - arm64
 
     steps:
       - uses: actions/checkout@v4
 
       - name: Build image
         run: |
-          rake docker:build arch=amd64 ruby_version=${{ matrix.ruby_version }} ubuntu_version=${{ matrix.ubuntu_version }}
+          rake docker:build arch=${{ matrix.arch }} ruby_version=${{ matrix.ruby_version }} ubuntu_version=${{ matrix.ubuntu_version }}
 
       - name: Check image
         run: |