enable Gradle wrapper validation

https://blog.gradle.org/gradle-wrapper-checksum-verification-github-action

.github/workflows/gradle.yml

@@ -16,6 +16,8 @@ jobs:
     name: Java ${{ matrix.java }} Build
     steps:
       - uses: actions/checkout@v2
+      - name: Gradle wrapper validation
+        uses: gradle/wrapper-validation-action@v1
       - name: Set up JDK ${{ matrix.java }}
         uses: actions/setup-java@v1
         with:

.github/workflows/publish-maven-central.yml

@@ -21,6 +21,9 @@ jobs:
     # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
     - uses: actions/checkout@v2
 
+    - name: Gradle wrapper validation
+      uses: gradle/wrapper-validation-action@v1
+
     # Runs a single command using the runners shell
     - name: Install gpg secret key
       run: |
@@ -39,4 +42,3 @@ jobs:
     - name: Display next step
       run: |
         echo "Now go to https://oss.sonatype.org/index.html#stagingRepositories, select the repo, Close it and then Release it"
-