Reintroduce cache in gha, add separate PR action

.github/workflows/gradle.yml

@@ -20,12 +20,12 @@ jobs:
       env:
         SIGNING_KEY: ${{ secrets.VIOLET_MOON_SIGNING_KEY }}
       run: echo "${SIGNING_KEY}" | gpg --import -
-    # - name: Cache
-    #   uses: actions/cache@v2
-    #   with:
-    #     path: |
-    #       ~/.gradle/caches
-    #     key: ${{ runner.os }}-gradle-${{ hashFiles('**/build.gradle', '**/gradle-wrapper.properties') }}
+    - name: Cache
+      uses: actions/cache@v2
+      with:
+        path: |
+          ~/.gradle/caches
+        key: ${{ runner.os }}-gradle-${{ hashFiles('**/build.gradle', '**/gradle-wrapper.properties') }}
     - name: Build with Gradle
       run: ./gradlew pmdMain spotlessJavaCheck build
     - name: PMD report

.github/workflows/pr.yml

@@ -0,0 +1,31 @@
+name: Pull Request CI
+
+on: [pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up JDK
+      uses: actions/setup-java@v2
+      with:
+        distribution: 'temurin'
+        java-version: '17'
+    - name: Validate gradlew integrity
+      uses: gradle/wrapper-validation-action@v1
+    - name: Cache
+      uses: actions/cache@v2
+      with:
+        path: |
+          ~/.gradle/caches
+        key: ${{ runner.os }}-gradle-${{ hashFiles('**/build.gradle', '**/gradle-wrapper.properties') }}
+    - name: Build with Gradle
+      run: ./gradlew pmdMain spotlessJavaCheck build
+    - name: PMD report
+      uses: jwgmeligmeyling/pmd-github-action@v1
+      if: failure()
+      with:
+        path: '**/reports/pmd/main.xml'
+    - name: Cleanup
+      run: ./gradlew --stop