Set Gradle version to 6 (compile, runtime, testCompile, and testRuntime are...

Set Gradle version to 6 (compile, runtime, testCompile, and testRuntime are deprecated and removed in version 7)

.gitlab-ci.yml

@@ -44,7 +44,7 @@ build_vollt_base_war:
   stage: build_base_war
   tags:
     - docker
-  image: gradle:jdk8
+  image: gradle:6-jdk8
   only:
     refs:
       - master

private-rows-extension/Dockerfile-build-env

-FROM gradle:jdk8
+FROM gradle:6-jdk8
 RUN apt-get update && apt install -y openjdk-17-jdk maven