patch 8.1.0529: flaky test sometimes fails in different ways

Problem:    Flaky test sometimes fails in different ways.
Solution:   When the second run gives a different error, try running the test
            again, up to five times.

src/version.c

@@ -792,6 +792,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    529,
 /**/
     528,
 /**/