Fix syntax highlighting in contrib guide.

anntzer · anntzer · commit eb776dde45f9 · 2021-12-20T11:46:08.000+01:00
(See other logging-output blocks, which are specified in the same way.)
diff --git a/doc/devel/contributing.rst b/doc/devel/contributing.rst
@@ -534,7 +534,9 @@ running the script::
     from matplotlib import my_matplotlib_module
     my_matplotlib_module.set_range(0, 0)  # set range
 
-will display::
+will display
+
+.. code-block:: none
 
     UserWarning: Attempting to set identical bottom==top
     warnings.warn('Attempting to set identical bottom==top')
