Get Oracle tests working again

[koppor]

The current docker image is too large for GitHub (2.6 GB for Oracle). We need to try other images. Example: https://github.com/bizybot/docker-oracle-xe-11g

This is a follow up for #6217.

[github-actions]

This issue has been inactive for half a year. Since JabRef is constantly evolving this issue may not be relevant any longer and it will be closed in two weeks if no further activity occurs.

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[koppor]

For me, testing is important. We should have test coverage. Therefore, we should work on this. We could also decide to drop Oracle support. However, there was much energy spent on it - and it theoretically works.

I think, the following image is good for testing: https://hub.docker.com/r/oracleinanutshell/oracle-xe-11g

We should move to Dockerunit probably: https://dockerunit.github.io/