patch 8.2.0339: Vim9: function return type may depend on arguments

Problem:    Vim9: function return type may depend on arguments.
Solution:   Instead of a fixed return type use a function to figure out the
            return type.

src/version.c

@@ -738,6 +738,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    339,
 /**/
     338,
 /**/