push.yml: update gradle/actions to v5

Author: stephengold

.github/workflows/push.yml

@@ -15,7 +15,7 @@ jobs:
           distribution: 'zulu'
           java-version: 17
       - uses: actions/checkout@v5
-      - uses: gradle/actions/wrapper-validation@v4
+      - uses: gradle/actions/wrapper-validation@v5
       - run: ./gradlew build --console=plain --stacktrace
 
   Java21-MacOS: