Merge pull request matplotlib#25484 from anntzer/tad

Deprecate tostring_rgb.

Author: ksunden

doc/api/next_api_changes/deprecations/XXXXX-AL.rst

@@ -0,0 +1,3 @@
+``RendererAgg.tostring_rgb`` and ``FigureCanvasAgg.tostring_rgb``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+... are deprecated with no replacement.

lib/matplotlib/backends/backend_agg.py

@@ -280,6 +280,7 @@ def buffer_rgba(self):
     def tostring_argb(self):
         return np.asarray(self._renderer).take([3, 0, 1, 2], axis=2).tobytes()
 
+    @_api.deprecated("3.8")
     def tostring_rgb(self):
         return np.asarray(self._renderer).take([0, 1, 2], axis=2).tobytes()
 
@@ -414,6 +415,7 @@ def get_renderer(self, cleared=False):
             self.renderer.clear()
         return self.renderer
 
+    @_api.deprecated("3.8")
     def tostring_rgb(self):
         """
         Get the image as RGB `bytes`.