ci: Use the previous build worker image in AppVeyor
ci: Use the previous build worker image in AppVeyor

This is a workaround as the recent Visual Studio 2019 image update
breaks our builds.

achow101/bitcoin,domob1812/bitcoin,tecnovert/particl-core,kallewoof/bitcoin,jnewbery/bitcoin,ElementsProject/elements,pstratem/bitcoin,EthanHeilman/bitcoin,rnicoll/dogecoin,kallewoof/bitcoin,fanquake/bitcoin,bitcoinknots/bitcoin,ajtowns/bitcoin,Xekyo/bitcoin,mruddy/bitcoin,bitcoinsSG/bitcoin,kallewoof/bitcoin,mruddy/bitcoin,namecoin/namecoin-core,fanquake/bitcoin,cdecker/bitcoin,dscotese/bitcoin,MarcoFalke/bitcoin,GroestlCoin/GroestlCoin,AkioNak/bitcoin,tecnovert/particl-core,jamesob/bitcoin,lateminer/bitcoin,EthanHeilman/bitcoin,sstone/bitcoin,fujicoin/fujicoin,domob1812/bitcoin,sstone/bitcoin,MeshCollider/bitcoin,jambolo/bitcoin,practicalswift/bitcoin,domob1812/namecore,particl/particl-core,kallewoof/bitcoin,kallewoof/bitcoin,bitcoin/bitcoin,dscotese/bitcoin,JeremyRubin/bitcoin,rnicoll/dogecoin,bitcoin/bitcoin,namecoin/namecore,Sjors/bitcoin,ElementsProject/elements,GroestlCoin/bitcoin,JeremyRubin/bitcoin,practicalswift/bitcoin,rnicoll/bitcoin,bitcoinsSG/bitcoin,mm-s/bitcoin,n1bor/bitcoin,andreaskern/bitcoin,pataquets/namecoin-core,jambolo/bitcoin,pstratem/bitcoin,mruddy/bitcoin,cdecker/bitcoin,qtumproject/qtum,domob1812/namecore,domob1812/bitcoin,ajtowns/bitcoin,mm-s/bitcoin,instagibbs/bitcoin,dscotese/bitcoin,particl/particl-core,JeremyRubin/bitcoin,achow101/bitcoin,lateminer/bitcoin,MarcoFalke/bitcoin,GroestlCoin/GroestlCoin,namecoin/namecoin-core,tecnovert/particl-core,rnicoll/dogecoin,JeremyRubin/bitcoin,mm-s/bitcoin,pataquets/namecoin-core,pataquets/namecoin-core,dscotese/bitcoin,rnicoll/bitcoin,jnewbery/bitcoin,GroestlCoin/bitcoin,apoelstra/bitcoin,GroestlCoin/bitcoin,jamesob/bitcoin,fujicoin/fujicoin,andreaskern/bitcoin,ElementsProject/elements,AkioNak/bitcoin,jlopp/statoshi,fanquake/bitcoin,apoelstra/bitcoin,n1bor/bitcoin,GroestlCoin/GroestlCoin,rnicoll/bitcoin,fanquake/bitcoin,GroestlCoin/bitcoin,n1bor/bitcoin,namecoin/namecore,cdecker/bitcoin,fujicoin/fujicoin,bitcoinknots/bitcoin,yenliangl/bitcoin,domob1812/namecore,sstone/bitcoin,fujicoin/fujicoin,Sjors/bitcoin,jambolo/bitcoin,anditto/bitcoin,instagibbs/bitcoin,pstratem/bitcoin,n1bor/bitcoin,particl/particl-core,sipsorcery/bitcoin,fujicoin/fujicoin,practicalswift/bitcoin,instagibbs/bitcoin,practicalswift/bitcoin,EthanHeilman/bitcoin,apoelstra/bitcoin,bitcoin/bitcoin,Xekyo/bitcoin,MeshCollider/bitcoin,particl/particl-core,apoelstra/bitcoin,ElementsProject/elements,ajtowns/bitcoin,particl/particl-core,anditto/bitcoin,jlopp/statoshi,achow101/bitcoin,bitcoinsSG/bitcoin,achow101/bitcoin,rnicoll/bitcoin,JeremyRubin/bitcoin,dscotese/bitcoin,rnicoll/bitcoin,litecoin-project/litecoin,qtumproject/qtum,jlopp/statoshi,ajtowns/bitcoin,GroestlCoin/GroestlCoin,prusnak/bitcoin,instagibbs/bitcoin,ajtowns/bitcoin,mruddy/bitcoin,namecoin/namecore,qtumproject/qtum,bitcoinknots/bitcoin,bitcoinsSG/bitcoin,bitcoin/bitcoin,Xekyo/bitcoin,GroestlCoin/bitcoin,Sjors/bitcoin,ajtowns/bitcoin,namecoin/namecore,prusnak/bitcoin,cdecker/bitcoin,fanquake/bitcoin,tecnovert/particl-core,pstratem/bitcoin,bitcoin/bitcoin,namecoin/namecoin-core,namecoin/namecoin-core,jambolo/bitcoin,qtumproject/qtum,fujicoin/fujicoin,prusnak/bitcoin,jamesob/bitcoin,yenliangl/bitcoin,lateminer/bitcoin,prusnak/bitcoin,bitcoin/bitcoin,mm-s/bitcoin,litecoin-project/litecoin,n1bor/bitcoin,qtumproject/qtum,apoelstra/bitcoin,jamesob/bitcoin,sipsorcery/bitcoin,achow101/bitcoin,namecoin/namecore,kallewoof/bitcoin,ElementsProject/elements,Xekyo/bitcoin,rnicoll/dogecoin,litecoin-project/litecoin,jamesob/bitcoin,jnewbery/bitcoin,pataquets/namecoin-core,bitcoinsSG/bitcoin,mruddy/bitcoin,namecoin/namecoin-core,mm-s/bitcoin,MeshCollider/bitcoin,jamesob/bitcoin,yenliangl/bitcoin,mm-s/bitcoin,rnicoll/bitcoin,jlopp/statoshi,EthanHeilman/bitcoin,mruddy/bitcoin,jlopp/statoshi,yenliangl/bitcoin,litecoin-project/litecoin,pstratem/bitcoin,rnicoll/dogecoin,MarcoFalke/bitcoin,sipsorcery/bitcoin,andreaskern/bitcoin,Sjors/bitcoin,sstone/bitcoin,domob1812/namecore,prusnak/bitcoin,yenliangl/bitcoin,namecoin/namecoin-core,AkioNak/bitcoin,anditto/bitcoin,sstone/bitcoin,n1bor/bitcoin,bitcoinknots/bitcoin,bitcoinknots/bitcoin,pataquets/namecoin-core,ElementsProject/elements,prusnak/bitcoin,jambolo/bitcoin,Sjors/bitcoin,jnewbery/bitcoin,achow101/bitcoin,domob1812/bitcoin,MarcoFalke/bitcoin,lateminer/bitcoin,qtumproject/qtum,domob1812/bitcoin,sstone/bitcoin,EthanHeilman/bitcoin,GroestlCoin/bitcoin,jnewbery/bitcoin,AkioNak/bitcoin,MeshCollider/bitcoin,instagibbs/bitcoin,jambolo/bitcoin,andreaskern/bitcoin,MarcoFalke/bitcoin,domob1812/namecore,cdecker/bitcoin,tecnovert/particl-core,andreaskern/bitcoin,lateminer/bitcoin,apoelstra/bitcoin,tecnovert/particl-core,pataquets/namecoin-core,domob1812/namecore,Xekyo/bitcoin,sipsorcery/bitcoin,MarcoFalke/bitcoin,litecoin-project/litecoin,EthanHeilman/bitcoin,jlopp/statoshi,qtumproject/qtum,cdecker/bitcoin,AkioNak/bitcoin,GroestlCoin/GroestlCoin,yenliangl/bitcoin,instagibbs/bitcoin,bitcoinsSG/bitcoin,namecoin/namecore,practicalswift/bitcoin,GroestlCoin/GroestlCoin,JeremyRubin/bitcoin,particl/particl-core,sipsorcery/bitcoin,domob1812/bitcoin,fanquake/bitcoin,lateminer/bitcoin,AkioNak/bitcoin,dscotese/bitcoin,litecoin-project/litecoin,MeshCollider/bitcoin,MeshCollider/bitcoin,anditto/bitcoin,practicalswift/bitcoin,anditto/bitcoin,anditto/bitcoin,pstratem/bitcoin,Xekyo/bitcoin,sipsorcery/bitcoin,andreaskern/bitcoin