sysutils/rubygem-facter: Fix with Ruby 3.4

base64 used to be a default gem, but starting with Ruby 3.4 it is not
anymore. Add this dependency explicitly to fix packages built with a
non-default version of Ruby.

Not bumping PORTREVISION as packages built against the default version
of Ruby have no issue and can wait for another reason to be rebuilt.

PR: 290261
Reported by: dvl
With hat: puppet