patch 8.2.3031: no error if a function name starts with an underscore

Problem:    No error if a function name starts with an underscore. (Naohiro
            Ono)
Solution:   In Vim9 script disallow a function name starting with an
            underscore, as is mentioned in the help. (closes #8414)
diff --git a/src/version.c b/src/version.c
index 0c3c887..77456bb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3031,
+/**/
     3030,
 /**/
     3029,