[test] Replace symlinks in legacy_cubes by real copies
This solves a "python setup.py build" issue on my machine.
Copying these files should not be a big deal because they
have been dropped in the "default" branch and we would not
touch them in 3.26 branch.
extend-diff-ignore = "^(__pkginfo__\.py$|doc/_themes/cubicweb/static/(logo-cubicweb-small\.svg|cubicweb\.ico|logo-cubicweb\.svg)$|cubicweb/(sobjects/test/data/(cubicweb_comment|cubicweb_card)|server/test/data-migractions/(migratedapp/)?(cubicweb_comment|cubicweb_localperms|cubicweb_basket|cubicweb_tag|cubicweb_card|cubicweb_file)|test/data-rewrite/(cubicweb_localperms|cubicweb_card))$|cubicweb\.spec$|setup\.cfg$|cubicweb/misc/cwfs)"