Create nested prefix test for #736
Create nested prefix test for #736

This test initializes two prefix context managers before using them.
Since the context is not entered immediately after initialization, the
test will fail if the bug is present.

xLegoz/fabric,jaraco/fabric,raimon49/fabric,rane-hs/fabric-py3,sdelements/fabric,ploxiln/fabric,kxxoling/fabric,likesxuqiang/fabric,itoed/fabric,SamuelMarks/fabric,getsentry/fabric,tekapo/fabric,opavader/fabric,elijah513/fabric,kmonsoor/fabric,pgroudas/fabric,bspink/fabric,bitprophet/fabric,MjAbuz/fabric,amaniak/fabric,cmattoon/fabric,pashinin/fabric,StackStorm/fabric,haridsv/fabric,hrubi/fabric,tolbkni/fabric,qinrong/fabric,rodrigc/fabric,fernandezcuesta/fabric,rbramwell/fabric,askulkarni2/fabric,cgvarela/fabric,TarasRudnyk/fabric,mathiasertl/fabric,bitmonk/fabric