Fix doctest parametrization for pytest 9.1

[rlratzel]

Summary

• Materialize the doctest generator before passing it to pytest.mark.parametrize.
• Update the copyright year for the touched test file.

Details

Pytest 9.1 deprecated passing non-Collection iterables, such as generators and iterators, as argvalues to pytest.mark.parametrize / metafunc.parametrize.
The pytest docs recommend converting generators and iterators to a list or tuple because they can otherwise be exhausted after one collection pass.

This repo also promotes DeprecationWarning to errors in python/cugraph/pytest.ini, so the new pytest warning can fail collection in pytest 9.1.x.
The doctest set is small, so eagerly materializing it is cheap and matches pytest's documented migration path.

References:

• https://docs.pytest.org/en/stable/changelog.html#pytest-9-1-0-2026-06-13
• https://docs.pytest.org/en/stable/deprecations.html#non-collection-iterables-in-pytest-mark-parametrize

Testing

• git diff --check upstream/main..HEAD
• docker exec 8cf097001d69 python -m pytest /Projects/cugraph/python/cugraph/cugraph/tests/docs/test_doctests.py --collect-only -q

Full doctest execution was also attempted in the provided container and failed due to missing local dataset files, for example karate.csv, unrelated to this collection-time change.

[alexbarghi-nv]

/merge