Fix return types of SliceLowLevelWCS
Fix return types of SliceLowLevelWCS

stargaser/astropy,saimn/astropy,StuartLittlefair/astropy,astropy/astropy,stargaser/astropy,lpsinger/astropy,pllim/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,MSeifert04/astropy,pllim/astropy,MSeifert04/astropy,saimn/astropy,lpsinger/astropy,astropy/astropy,mhvk/astropy,saimn/astropy,lpsinger/astropy,larrybradley/astropy,aleksandr-bakanov/astropy,dhomeier/astropy,MSeifert04/astropy,stargaser/astropy,larrybradley/astropy,pllim/astropy,pllim/astropy,saimn/astropy,saimn/astropy,aleksandr-bakanov/astropy,mhvk/astropy,mhvk/astropy,MSeifert04/astropy,mhvk/astropy,dhomeier/astropy,astropy/astropy,larrybradley/astropy,aleksandr-bakanov/astropy,stargaser/astropy,dhomeier/astropy,dhomeier/astropy,pllim/astropy,lpsinger/astropy,StuartLittlefair/astropy,dhomeier/astropy,mhvk/astropy,lpsinger/astropy,astropy/astropy,larrybradley/astropy,StuartLittlefair/astropy,aleksandr-bakanov/astropy,astropy/astropy,larrybradley/astropy