Run spotless on PR

We recently added Java code to this package to support performance
tests. To ensure we maintain a high bar for code quality, we enabled
spotless and in this commit, we enable running spotless on all PRs.

.github/workflows/pr_build.yml

@@ -66,4 +66,25 @@ jobs:
           run_unit_tests: false
 
       - name: Run ${{ matrix.tox-environment }} with tox
-        run: tox -e ${{ matrix.tox-environment }}
+        run: tox -e ${{ matrix.tox-environment }}
+
+  spotless:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Contrib Repo @ SHA - ${{ github.sha }}
+        uses: actions/checkout@v4
+
+      - name: Gradle validation
+        uses: gradle/wrapper-validation-action@v1
+
+      - name: Set up Java
+        uses: actions/setup-java@v4
+        with:
+          java-version: 17
+          distribution: temurin
+
+      - name: Setup Gradle
+        uses: gradle/gradle-build-action@v3
+
+      - name: Build with Gradle
+        run: cd performance-tests; ./gradlew spotlessCheck