matplotlib.cm.get_cmap is deprecated and will be removed in Matplotlib 3.11

[ivankrylov]

src/graphing/heatmap.py:113 calls matplotlib.cm.get_cmap, which emits on every
heatmap plot:
MatplotlibDeprecationWarning: The get_cmap function was deprecated in Matplotlib 3.7
and will be removed in 3.11. Use matplotlib.colormaps[name] or
matplotlib.colormaps.get_cmap() or pyplot.get_cmap() instead.
Reproduces on the current notebooks (cells calling plot_heatmaps and
plot_heatmaps_logarithmic in both GCGC.ipynb and FeatureExamples.ipynb). Both
heatmap functions will break outright once users upgrade to Matplotlib 3.11.