ENV.rb: Always return integers from make_jobs
ENV.rb: Always return integers from make_jobs

When referencing `Hardware.processor_count`, `ENV.make_jobs` will return an
integer. If referencing the environment variable `HOMEBREW_MAKE_JOBS`, it
returned a string.

Now, the function always returns an integer.

Fixes Homebrew/homebrew#12033.

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