Correct “an” → “a” with “Unicode”, “user”, “UTF”, etc

This affects documentation and code comments.
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index 7e74607..c104098 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -492,7 +492,7 @@
         return key;
     }
     else {
-        /* for other types, use the object identifier as an unique identifier
+        /* for other types, use the object identifier as a unique identifier
          * to ensure that they are seen as unequal. */
         PyObject *obj_id = PyLong_FromVoidPtr(op);
         if (obj_id == NULL)