Fixed doctests that failed due to error message being updated.

Author: Noel Roemmele

src/sage/categories/enumerated_sets.py

@@ -432,7 +432,7 @@ def __getitem__(self, i):
                 sage: P[-1]
                 Traceback (most recent call last):
                 ...
-                NotImplementedError: cannot list an infinite set
+                ValueError: infinite list
 
             ::
 

src/sage/sets/finite_enumerated_set.py

@@ -288,7 +288,7 @@ def unrank(self, i):
             sage: S[-4]
             Traceback (most recent call last):
             ...
-            IndexError: list index out of range
+            IndexError: index out of range
         """
         return self._elements[i]