Replace final test of python 3.8 by moving initial test to that version.
Replace final test of python 3.8 by moving initial test to that version.

pllim/astropy,aleksandr-bakanov/astropy,astropy/astropy,astropy/astropy,pllim/astropy,astropy/astropy,dhomeier/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,aleksandr-bakanov/astropy,pllim/astropy,lpsinger/astropy,mhvk/astropy,astropy/astropy,pllim/astropy,StuartLittlefair/astropy,dhomeier/astropy,lpsinger/astropy,lpsinger/astropy,pllim/astropy,astropy/astropy,mhvk/astropy,dhomeier/astropy,aleksandr-bakanov/astropy,lpsinger/astropy,aleksandr-bakanov/astropy,saimn/astropy,larrybradley/astropy,dhomeier/astropy,dhomeier/astropy,larrybradley/astropy,StuartLittlefair/astropy,saimn/astropy,saimn/astropy,saimn/astropy,larrybradley/astropy,mhvk/astropy,mhvk/astropy,larrybradley/astropy,mhvk/astropy,larrybradley/astropy,StuartLittlefair/astropy,lpsinger/astropy,saimn/astropy