patch 8.1.1488: summary of tests has incorrect failed count

Problem:    Summary of tests has incorrect failed count.
Solution:   Add to the failed count instead of setting it. (Christian Brabandt)
diff --git a/src/version.c b/src/version.c
index 5ac6f9d..90ee247 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1488,
+/**/
     1487,
 /**/
     1486,