[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.
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Changelog history
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.. include:: 3.26.rst
.. include:: 3.25.rst
.. include:: 3.24.rst
.. include:: 3.23.rst
.. include:: 3.22.rst
.. include:: 3.21.rst
.. include:: 3.20.rst
.. include:: 3.19.rst
.. include:: 3.18.rst
.. include:: 3.17.rst
.. include:: 3.16.rst
.. include:: 3.15.rst
.. include:: 3.14.rst