bpo-35044, doc: Use the :exc: role for the exceptions (GH-10037)

diff --git a/Doc/faq/design.rst b/Doc/faq/design.rst
index 5e54df6..e2d63a0 100644
--- a/Doc/faq/design.rst
+++ b/Doc/faq/design.rst
@@ -528,7 +528,7 @@
      mydict = {[1, 2]: '12'}
      print(mydict[[1, 2]])
 
-  would raise a KeyError exception because the id of the ``[1, 2]`` used in the
+  would raise a :exc:`KeyError` exception because the id of the ``[1, 2]`` used in the
   second line differs from that in the first line.  In other words, dictionary
   keys should be compared using ``==``, not using :keyword:`is`.