Update GitHub Actions

- Wrapper validation is done as part of setup-gradle, no need to do it
  ourselves, see https://github.com/gradle/actions/blob/main/docs/setup-gradle.md#gradle-wrapper-validation
- Enable storing configuration cache accross builds
- Cache build outputs as well to reduce build time

.github/workflows/build.yml

@@ -22,10 +22,10 @@ jobs:
         with:
           distribution: "temurin"
           java-version: "17"
-      - name: "Gradle Wrapper validation"
-        uses: gradle/actions/wrapper-validation@v4
       - name: "Setup Gradle"
         uses: gradle/actions/setup-gradle@v4
+        with:
+          cache-encryption-key: ${{ secrets.GradleEncryptionKey }}
       - name: "Setup matchers"
         run: |
           # Setting up matchers...
@@ -43,6 +43,14 @@ jobs:
               echo "Matcher configured: ${NAME:?}"
             fi
           done
+      - name: "Cache Gradle build output"
+        uses: actions/cache@v4
+        with:
+          path: |
+            **/build
+          key: gradle-build-v1-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+          restore-keys: |
+            gradle-build-v1-
       - name: "Inspect Gradle tasks"
         run: "./gradlew tasks"
       - name: "Execute Gradle assemble"