Prevent installing an already installed Java version

What does this MR do?

SDKMAN introduced a breaking change in 5.3.4 where it now exits with exit code 1 when trying to install a version that's already installed. We were relying on this by chaining the source && install && default commands, but now it fails and doesn't get to default anymore, thus not setting the proper Java version.

P.S: I did some basic tests on this branch for the following:

1. Java 11 - successful job
2. Java 8 - successful job
3. Invalid Java version - successful job with the invalid warning and fallback to 8

What are the relevant issue numbers?

gitlab-org/gitlab#205696 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template (also in CE)
  • Job definition example
  • CI Templates (to be removed)
  • Vendored CI Templates (also in CE)
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer