update-report: tweak Cask migration output.
update-report: tweak Cask migration output.

No longer output every cask under the list of changed formulae but
instead create a dedicated, unprinted report section for casks and then
iterate through that instead.

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