optimize test runtime

[SimeonEhrig]

I checked the following CI job from our dev branch: https://gitlab.com/hzdr/crp/alpaka/-/jobs/7619007751
All tests together takes 8 minutes to run. There are a few tests, which takes a big amount of time. If I'm not wrong, these should almost be examples. I believe to problem size are to big. Somebody should check, if my assumption is correct. If yes, we need to check if the problem size is required to verify the correct behavior and if this is not necessary ether we can decrease the problem size in source code or set it via application argument and ctest command.