sift: Update for Go 1.16 (#71687)
sift: Update for Go 1.16 (#71687)

* sift: Set GO111MODULE=auto for Go 1.16

This will allow this package to build with Go 1.16.

Epic: #47627

* sift: Resolve deprecated SPDX license

https://github.com/svent/sift/blob/master/LICENSE appears to be GPL 3.0;
update the license for the sift formula to match.
makigumo/homebrew-core,Moisan/homebrew-core,lemzwerg/homebrew-core,adam-moss/homebrew-core,spaam/homebrew-core,nbari/homebrew-core,nandub/homebrew-core,filcab/homebrew-core,chrisfinazzo/homebrew-core,mfikes/homebrew-core,Linuxbrew/homebrew-core,stgraber/homebrew-core,sjackman/homebrew-core,cblecker/homebrew-core,uyjulian/homebrew-core,mbcoguno/homebrew-core,filcab/homebrew-core,chrisfinazzo/homebrew-core,mbcoguno/homebrew-core,makigumo/homebrew-core,nbari/homebrew-core,JCount/homebrew-core,zyedidia/homebrew-core,JCount/homebrew-core,mbcoguno/homebrew-core,cblecker/homebrew-core,Linuxbrew/homebrew-core,spaam/homebrew-core,Homebrew/homebrew-core,zyedidia/homebrew-core,nandub/homebrew-core,uyjulian/homebrew-core,Moisan/homebrew-core,lemzwerg/homebrew-core,sjackman/homebrew-core,adam-moss/homebrew-core,mfikes/homebrew-core,stgraber/homebrew-core,Homebrew/homebrew-core