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.
diff --git a/src/version.c b/src/version.c
index e72adfc..ebea70f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    529,
+/**/
     528,
 /**/
     527,