patch 9.0.0620: matchaddpos() can only add up to 8 matches

Problem:    matchaddpos() can only add up to 8 matches.
Solution:   Allocate the array of positions. (closes #11248)
diff --git a/src/version.c b/src/version.c
index 276b37a..e264b55 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    620,
+/**/
     619,
 /**/
     618,