virtualenv==20.0.0 introduced new symlinking of "seed" packages that
broke within a bwrap context. We fixed this by forcing those seed
packages to be installed by pip avoiding any symlinking. Since then
upstream virtualenv has realize this was bad default behavior and
virtualenv==20.0.2 does not symlink by default.
Take advantage of this and exclude 20.0.0 and 20.0.1 as they need
special handling. This allows other versions (new and old) to function.