workflows/tests: link python@3.8.
workflows/tests: link python@3.8.

Investigated a full uninstall but it takes too long (>5m).

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