test_corsika_histograms_visualize.py::test_kernel_plot_2d_photons Warnings

[GernotMaier]

tests/unit_tests/corsika/test_corsika_histograms_visualize.py::test_kernel_plot_2d_photons[5-5]
  /Users/maierg/DESYCloud/CTA/Pipelines/MC-Pipeline/gammasim-tools/simtools/tests/unit_tests/corsika/test_corsika_histograms_visualize.py:23: RuntimeWarning: More than 20 figures have been opened. Figures created through the pyplot interface (`matplotlib.pyplot.figure`) are retained until explicitly closed and may consume too much memory. (To control this warning, see the rcParam `figure.max_open_warning`). Consider using `matplotlib.pyplot.close()`.

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

This should be addressed.