Fix Header.update tests
Fix Header.update tests

Looks like update with the dict syntax is triggering HIERARCH warnings, though
it was not the case with the old syntax.

dhomeier/astropy,mhvk/astropy,kelle/astropy,lpsinger/astropy,joergdietrich/astropy,astropy/astropy,MSeifert04/astropy,StuartLittlefair/astropy,bsipocz/astropy,saimn/astropy,pllim/astropy,pllim/astropy,aleksandr-bakanov/astropy,dhomeier/astropy,mhvk/astropy,funbaker/astropy,tbabej/astropy,dhomeier/astropy,tbabej/astropy,pllim/astropy,kelle/astropy,larrybradley/astropy,larrybradley/astropy,joergdietrich/astropy,aleksandr-bakanov/astropy,AustereCuriosity/astropy,pllim/astropy,mhvk/astropy,AustereCuriosity/astropy,dhomeier/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,lpsinger/astropy,astropy/astropy,MSeifert04/astropy,lpsinger/astropy,bsipocz/astropy,stargaser/astropy,lpsinger/astropy,tbabej/astropy,bsipocz/astropy,pllim/astropy,larrybradley/astropy,tbabej/astropy,astropy/astropy,saimn/astropy,saimn/astropy,DougBurke/astropy,saimn/astropy,mhvk/astropy,AustereCuriosity/astropy,joergdietrich/astropy,stargaser/astropy,kelle/astropy,aleksandr-bakanov/astropy,dhomeier/astropy,DougBurke/astropy,DougBurke/astropy,kelle/astropy,joergdietrich/astropy,AustereCuriosity/astropy,larrybradley/astropy,funbaker/astropy,lpsinger/astropy,StuartLittlefair/astropy,larrybradley/astropy,tbabej/astropy,StuartLittlefair/astropy,AustereCuriosity/astropy,astropy/astropy,stargaser/astropy,MSeifert04/astropy,bsipocz/astropy,saimn/astropy,DougBurke/astropy,astropy/astropy,aleksandr-bakanov/astropy,stargaser/astropy,funbaker/astropy,MSeifert04/astropy,funbaker/astropy,mhvk/astropy,kelle/astropy,joergdietrich/astropy