ci: use GCC 8 when building packages in native_qt5 CI
ci: use GCC 8 when building packages in native_qt5 CI

Our minimum required GCC is GCC 8, and this change in required for
changes like #23839 which take advantage of flags introduced in that
version of GCC.

This should have been included as part of
182de7ba10811ec39e24ec5bec7cd2119f776f2f.

fujicoin/fujicoin,pataquets/namecoin-core,mruddy/bitcoin,lateminer/bitcoin,namecoin/namecore,kallewoof/bitcoin,fanquake/bitcoin,bitcoinknots/bitcoin,tecnovert/particl-core,AkioNak/bitcoin,GroestlCoin/bitcoin,instagibbs/bitcoin,particl/particl-core,GroestlCoin/GroestlCoin,particl/particl-core,sipsorcery/bitcoin,domob1812/bitcoin,fanquake/bitcoin,achow101/bitcoin,bitcoin/bitcoin,mm-s/bitcoin,kallewoof/bitcoin,anditto/bitcoin,bitcoinsSG/bitcoin,namecoin/namecore,namecoin/namecoin-core,tecnovert/particl-core,dscotese/bitcoin,jamesob/bitcoin,domob1812/namecore,jambolo/bitcoin,jlopp/statoshi,andreaskern/bitcoin,jamesob/bitcoin,domob1812/bitcoin,Xekyo/bitcoin,bitcoin/bitcoin,jlopp/statoshi,bitcoin/bitcoin,mruddy/bitcoin,domob1812/namecore,fujicoin/fujicoin,ajtowns/bitcoin,pataquets/namecoin-core,mruddy/bitcoin,bitcoinsSG/bitcoin,domob1812/bitcoin,anditto/bitcoin,bitcoinsSG/bitcoin,domob1812/bitcoin,andreaskern/bitcoin,lateminer/bitcoin,jlopp/statoshi,pataquets/namecoin-core,namecoin/namecore,domob1812/bitcoin,AkioNak/bitcoin,ajtowns/bitcoin,mm-s/bitcoin,GroestlCoin/bitcoin,GroestlCoin/GroestlCoin,particl/particl-core,lateminer/bitcoin,AkioNak/bitcoin,mm-s/bitcoin,pataquets/namecoin-core,particl/particl-core,bitcoinsSG/bitcoin,jamesob/bitcoin,dscotese/bitcoin,ajtowns/bitcoin,bitcoinknots/bitcoin,GroestlCoin/GroestlCoin,kallewoof/bitcoin,pataquets/namecoin-core,anditto/bitcoin,bitcoinknots/bitcoin,Xekyo/bitcoin,fujicoin/fujicoin,anditto/bitcoin,sipsorcery/bitcoin,domob1812/namecore,sipsorcery/bitcoin,achow101/bitcoin,bitcoinsSG/bitcoin,ajtowns/bitcoin,sipsorcery/bitcoin,bitcoinknots/bitcoin,Xekyo/bitcoin,instagibbs/bitcoin,sstone/bitcoin,fanquake/bitcoin,ajtowns/bitcoin,Xekyo/bitcoin,AkioNak/bitcoin,namecoin/namecoin-core,instagibbs/bitcoin,anditto/bitcoin,jambolo/bitcoin,GroestlCoin/bitcoin,tecnovert/particl-core,andreaskern/bitcoin,namecoin/namecoin-core,bitcoin/bitcoin,tecnovert/particl-core,GroestlCoin/GroestlCoin,mm-s/bitcoin,kallewoof/bitcoin,GroestlCoin/GroestlCoin,namecoin/namecoin-core,dscotese/bitcoin,dscotese/bitcoin,sipsorcery/bitcoin,fujicoin/fujicoin,domob1812/bitcoin,lateminer/bitcoin,jamesob/bitcoin,fujicoin/fujicoin,bitcoinsSG/bitcoin,namecoin/namecoin-core,Xekyo/bitcoin,Xekyo/bitcoin,achow101/bitcoin,GroestlCoin/bitcoin,sstone/bitcoin,instagibbs/bitcoin,dscotese/bitcoin,mm-s/bitcoin,tecnovert/particl-core,andreaskern/bitcoin,jlopp/statoshi,kallewoof/bitcoin,particl/particl-core,instagibbs/bitcoin,fujicoin/fujicoin,lateminer/bitcoin,namecoin/namecore,jlopp/statoshi,jambolo/bitcoin,anditto/bitcoin,namecoin/namecoin-core,mruddy/bitcoin,fanquake/bitcoin,bitcoin/bitcoin,GroestlCoin/bitcoin,sstone/bitcoin,jambolo/bitcoin,AkioNak/bitcoin,jamesob/bitcoin,sstone/bitcoin,domob1812/namecore,sipsorcery/bitcoin,jambolo/bitcoin,mruddy/bitcoin,sstone/bitcoin,bitcoinknots/bitcoin,dscotese/bitcoin,fanquake/bitcoin,ajtowns/bitcoin,mm-s/bitcoin,andreaskern/bitcoin,particl/particl-core,domob1812/namecore,bitcoin/bitcoin,GroestlCoin/bitcoin,AkioNak/bitcoin,achow101/bitcoin,lateminer/bitcoin,kallewoof/bitcoin,andreaskern/bitcoin,tecnovert/particl-core,fanquake/bitcoin,namecoin/namecore,mruddy/bitcoin,achow101/bitcoin,jamesob/bitcoin,namecoin/namecore,GroestlCoin/GroestlCoin,pataquets/namecoin-core,jambolo/bitcoin,instagibbs/bitcoin,achow101/bitcoin,domob1812/namecore,sstone/bitcoin,jlopp/statoshi