Add workflow job for macOS.

.github/workflows/go.yml

@@ -10,6 +10,21 @@ on:
     branches: [ "master" ]
 
 jobs:
+  build:
+    runs-on: macos-latest
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Set up Go
+      uses: actions/setup-go@v4
+      with:
+        go-version: '1.21'
+
+    - name: Build
+      run: go build -v ./...
+
+    - name: Test
+      run: go test -v ./...
 
   build:
     runs-on: ubuntu-latest