Add job that tests the produced images

[awesomebytes]

It should just try to extract the released version and execute something meaningful.
Another one that would use 'the latest release' would also be good.

This will avoid faulty releases as sometimes they don't work cause:

• We ran out of disk space at some point and we are missing some split file (Hopefully I fixed this issue already)
• The upload to GitHub releases returned some error. For some reason this doesn't crash the job.
• Some other unknown error that I haven't yet encountered.

[awesomebytes]

Probably creating md5 files would help too.