versioned_keg_only_allowlist: add Python 3.10
versioned_keg_only_allowlist: add Python 3.10

Previous changes allow Python 3.9 and Python 3.10 to be linked at the
same time.

nandub/homebrew-core,adam-moss/homebrew-core,chrisfinazzo/homebrew-core,Homebrew/homebrew-core,filcab/homebrew-core,adam-moss/homebrew-core,makigumo/homebrew-core,chrisfinazzo/homebrew-core,stgraber/homebrew-core,makigumo/homebrew-core,filcab/homebrew-core,nbari/homebrew-core,Homebrew/homebrew-core,sjackman/homebrew-core,sjackman/homebrew-core,lemzwerg/homebrew-core,stgraber/homebrew-core,lemzwerg/homebrew-core,nandub/homebrew-core,nbari/homebrew-core