rails-completion: add livecheck
rails-completion: add livecheck

`rails-completion` uses the same repository as `ruby-completion` and
`brew livecheck` should skip it for the same reasons (see:
Homebrew/homebrew-core#80895).
mfikes/homebrew-core,Homebrew/homebrew-core,stgraber/homebrew-core,chrisfinazzo/homebrew-core,uyjulian/homebrew-core,mbcoguno/homebrew-core,zyedidia/homebrew-core,cblecker/homebrew-core,mbcoguno/homebrew-core,makigumo/homebrew-core,chrisfinazzo/homebrew-core,Homebrew/homebrew-core,mbcoguno/homebrew-core,sjackman/homebrew-core,zyedidia/homebrew-core,lemzwerg/homebrew-core,cblecker/homebrew-core,adam-moss/homebrew-core,filcab/homebrew-core,sjackman/homebrew-core,nandub/homebrew-core,Moisan/homebrew-core,filcab/homebrew-core,lemzwerg/homebrew-core,nbari/homebrew-core,nbari/homebrew-core,uyjulian/homebrew-core,nandub/homebrew-core,makigumo/homebrew-core,mfikes/homebrew-core,stgraber/homebrew-core,adam-moss/homebrew-core,Moisan/homebrew-core