The 3.3 branch is on SVN and it will stay there. 3.3 is already 2 versions behind, so I don't think it's going to be maintained.
I can't access SVN since a few days ago. Maybe the url changed or the SVN isn't working anymore because the migration to git?
I noticed that hibernate-core 3.3 branch is on github now (but envers wasn't inside core on that version).