The Koji test in Github actions was always a bit quick and dirty solution.
I think it's much nicer solution to run it on Schutzbot.
Therefore, this commit moves the koji_test.go to a new osbuild-koji-tests
executable. This new test isn't run in the base test suite as one would
anticipate but inside the koji.sh test. This is needed because
osbuild-koji-tests requires a running koji instance. This might change
in the future but I think it works for now.
