Enable tests on PRs

It only executes unit tests.

Checkstyle and Spring Java Format are executed.

.github/workflows/pr-check.yml

@@ -0,0 +1,25 @@
+name: PR Check
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  build:
+    name: Build branch
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout source code
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v4
+        with:
+          java-version: '17'
+          distribution: 'temurin'
+          cache: 'maven'
+
+      - name: Run tests
+        run: |
+          ./mvnw test