test-bot: prune cache after 7 days.
test-bot: prune cache after 7 days.

Closes Homebrew/homebrew#42892.

Signed-off-by: Mike McQuaid <a17fed27eaa842282862ff7c1b9c8395a26ac320@mikemcquaid.com>

tonyg/homebrew,konqui/brew,ilovezfs/brew,mahori/brew,tonyg/homebrew,sjackman/homebrew,Linuxbrew/brew,DomT4/brew,hanxue/linuxbrew,gordonmcshane/homebrew,maxim-belkin/brew,konqui/brew,toonetown/homebrew,nandub/brew,zmwangx/brew,JCount/brew,jmsundar/brew,AnastasiaSulyagina/brew,Homebrew/brew,bfontaine/brew,amar-laksh/brew_sudo,aw1621107/brew,mgrimes/brew,sjackman/homebrew,palxex/brew,Linuxbrew/brew,MikeMcQuaid/brew,mahori/brew,mistydemeo/homebrew,reitermarkus/brew,EricFromCanada/brew,gordonmcshane/homebrew,vitorgalvao/brew,rwhogg/brew,staticfloat/brew,amar-laksh/brew_sudo,reitermarkus/brew,jmsundar/brew,alyssais/brew,maxim-belkin/brew,mgrimes/brew,mgrimes/brew,JCount/brew,reelsense/brew,claui/brew,ilovezfs/brew,zmwangx/brew,alyssais/brew,vitorgalvao/brew,rwhogg/brew,rwhogg/brew,claui/brew,pseudocody/brew,gregory-nisbet/brew,hanxue/linuxbrew,nandub/brew,muellermartin/dist,amar-laksh/brew_sudo,reitermarkus/brew,hanxue/linuxbrew,konqui/brew,MikeMcQuaid/brew,AnastasiaSulyagina/brew,reitermarkus/brew,bfontaine/brew,staticfloat/brew,pseudocody/brew,nandub/brew,DomT4/brew,mistydemeo/homebrew,DomT4/brew,MikeMcQuaid/brew,aw1621107/brew,toonetown/homebrew,ilovezfs/brew,toonetown/homebrew,palxex/brew,JCount/brew,Homebrew/brew,claui/brew,mahori/brew,EricFromCanada/brew,sjackman/homebrew,konqui/brew,mahori/brew,alyssais/brew,staticfloat/brew,muellermartin/dist,reelsense/brew,maxim-belkin/brew,jmsundar/brew,palxex/brew,Homebrew/brew,vitorgalvao/brew,Homebrew/brew,gregory-nisbet/brew,bfontaine/brew,claui/brew,Linuxbrew/brew,tonyg/homebrew,AnastasiaSulyagina/brew,EricFromCanada/brew,gordonmcshane/homebrew,sjackman/homebrew,zmwangx/brew,pseudocody/brew,MikeMcQuaid/brew,gregory-nisbet/brew,aw1621107/brew,Linuxbrew/brew,JCount/brew,DomT4/brew,reelsense/brew,EricFromCanada/brew,muellermartin/dist,vitorgalvao/brew,mistydemeo/homebrew,nandub/brew