update ctest configuration for EventLoop tests

There are several packages that sort of belong together in terms of testing, in particular I had previously moved several tests from the other packages into EventLoopTest, because they required to link against all packages. So now these tests should run in the CI whenever any of the packages is updated.

This isn't the prettiest cmake implementation available, the problem is that the pretty implementation of just adding it to the list of properties when calling atlas_add_test created hard to understand cmake errors (actually semi-randomly working and failing based on the exact list of labels passed 🤔). @akraszna may want to comment, but I suspect that adding labels to tests is currently not supported via atlas_add_test.