GitDownloadStrategy: allow disabling of shallow clone
GitDownloadStrategy: allow disabling of shallow clone

Closes Homebrew/homebrew#25751.
Closes Homebrew/homebrew#26730.

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