patch 8.0.0471: exit callback test sometimes fails

Problem:    Exit callback test sometimes fails.
Solution:   Add it to the list of flaky tests.

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    471,
 /**/
     470,
 /**/