Libelektra: Jenkins: build timeouts

The following build message occurred in multiple PRs I have seen (e.g. #3150):

Sending interrupt signal to process

Terminated

It seems that we are increasingly hitting the 10 minute Jenkins limit (when a build has no log output for 10 minutes). https://github.com/ElektraInitiative/libelektra/blob/6aea503521a35cbeef3a719f8c73c2fe40830c1d/scripts/jenkins/Jenkinsfile#L1271

I'm not sure it will help to increase the limit, as some of the killed jobs show that they are running for 5+ hours. We can try to increase the limit and see whether we are only exceeding it by very little. Otherwise I think we will need to evaluate what's causing the builds to take forever and work on a better solution.

The fact that many builds are currently failing (and being re-built) because of problems with our Jenkins ironically puts even more load on the systems, so the effect seems to amplify.