Moving up to maven-3.8.2-jdk-8

We need this in the maven-release-candidates.yml file to be able to use HTTPS git URLs, since the old 3.3.9 maven container has outdated ones. But, the new container uses python3 instead of python, so we have to edit the before_script. It is easier just to move everything up and be consistent.

If 3.3.9 is required for a specific project, the mvnw logic is still respected. Add an appropriate maven wrapper to the project, and that version will be used instead.