ctest unit tests are run twice

[LecrisUT]

If I read this part correctly

https://github.com/xtensor-stack/xtl/blob/174e99da6e27c3ee5837fb74e7e65330af4cd2a6/test/CMakeLists.txt#L120-L135

The ctest would run eact test twice, once in xtest and once in ${targetname}. Why not get rid of the former?

Also the custom target calling test_xtl is not very efficient because it would not be parallelized. I've seen implementations where the target is just a thin wrapper around ctest with appropriate filters/environment variables.