ci/test: run mvn verify for every PR and merge to main

Fixes #39

.github/workflows/test.yml

@@ -0,0 +1,28 @@
+name: Test
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    services:
+      emulator:
+        image: gcr.io/cloud-spanner-emulator/emulator:latest
+        ports:
+          - 9010:9010
+          - 9020:9020
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+      - name: Use Java 17
+        uses: actions/setup-java@v3
+        with:
+          distribution: 'temurin'
+          java-version: '17'
+          cache: 'maven'
+      - name: Run the Maven verify phase
+        run: mvn --batch-mode --update-snapshots verify