tests.yml: use proper matrix syntax
tests.yml: use proper matrix syntax

Co-authored-by: Bo Anderson <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@boanderson.me>

nandub/brew,MikeMcQuaid/brew,MikeMcQuaid/brew,reitermarkus/brew,konqui/brew,nandub/brew,Homebrew/brew,Homebrew/brew,claui/brew,mahori/brew,claui/brew,nandub/brew,mahori/brew,sjackman/homebrew,MikeMcQuaid/brew,EricFromCanada/brew,JCount/brew,konqui/brew,Homebrew/brew,Homebrew/brew,reitermarkus/brew,vitorgalvao/brew,claui/brew,JCount/brew,EricFromCanada/brew,reitermarkus/brew,vitorgalvao/brew,EricFromCanada/brew,sjackman/homebrew,JCount/brew,mahori/brew,nandub/brew,MikeMcQuaid/brew,konqui/brew,sjackman/homebrew,sjackman/homebrew,EricFromCanada/brew,vitorgalvao/brew,reitermarkus/brew,konqui/brew,JCount/brew,vitorgalvao/brew,mahori/brew,claui/brew