specutils v1.5 cause major break

Chris found out that v1.5 (fortunately currently only on conda-forge) is very different from v1.1 and seriously breaks thing.  It will be a big job to fix that one to bring compatibility again.  (Or that's my understanding.)

So, next 3.0.x patch release, if that is not fixed, (likely not to be) we will need to pin specutils to 1.1 instead of the current >=1.1.