Merge pull request matplotlib#19766 from QuLogic/extend-cmap-deprecation

Set colormap modification removal to 3.6.

Author: anntzer

lib/matplotlib/colors.py

@@ -557,10 +557,12 @@ def _warn_if_global_cmap_modified(cmap):
     if getattr(cmap, '_global', False):
         _api.warn_deprecated(
             "3.3",
+            removal="3.6",
             message="You are modifying the state of a globally registered "
-                    "colormap. In future versions, you will not be able to "
-                    "modify a registered colormap in-place. To remove this "
-                    "warning, you can make a copy of the colormap first. "
+                    "colormap. This has been deprecated since %(since)s and "
+                    "%(removal)s, you will not be able to modify a "
+                    "registered colormap in-place. To remove this warning, "
+                    "you can make a copy of the colormap first. "
                     f'cmap = mpl.cm.get_cmap("{cmap.name}").copy()'
         )