This method is only available on newer versions.
The first available version (v2_6_3) is shown here.
double_check_for(*)
public
it’s possible that gems from one source depend on gems from some other
source, so now we download gemspecs and iterate over those dependencies,
looking for gems we don’t have info on yet.
# File lib/bundler/source.rb, line 39
def double_check_for(*); end