Document that get_cmap returns a copy now

QuLogic · QuLogic · commit 2a1da87b73fb · 2022-08-22T21:37:18.000-04:00
This was put into effect in #22298, but was not given an API note.
diff --git a/doc/api/next_api_changes/behavior/23710-ES.rst b/doc/api/next_api_changes/behavior/23710-ES.rst
@@ -0,0 +1,7 @@
+``plt.get_cmap`` and ``matplotlib.cm.get_cmap`` return a copy
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Formerly, `~.pyplot.get_cmap` and `.cm.get_cmap` returned a global version of a
+`.Colormap`. This was prone to errors as modification of the colormap would
+propagate from one location to another without warning. Now, a new copy of the
+colormap is returned.
