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)

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3031,
 /**/
     3030,
 /**/