Fix typo: class declaration (GH-11678)

(cherry picked from commit dfc8bb987d1fcba9225a19542c0fb9132b846b5b)

Co-authored-by: nu_no <nuno.an@gmail.com>
diff --git a/Doc/library/enum.rst b/Doc/library/enum.rst
index 81e9766..a6285ff 100644
--- a/Doc/library/enum.rst
+++ b/Doc/library/enum.rst
@@ -394,7 +394,7 @@
 data type, and as many :class:`object`-based mixin classes as needed.  The
 order of these base classes is::
 
-    def EnumName([mix-in, ...,] [data-type,] base-enum):
+    class EnumName([mix-in, ...,] [data-type,] base-enum):
         pass
 
 Also, subclassing an enumeration is allowed only if the enumeration does not define