patch 8.2.1720: Vim9: memory leak with heredoc that isn't executed

Problem:    Vim9: memory leak with heredoc that isn't executed. (Dominique
            Pellé)
Solution:   Don't clear the list items. (closes #6991)
diff --git a/src/version.c b/src/version.c
index 15c4976..a5cb6a8 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1720,
+/**/
     1719,
 /**/
     1718,