patch 8.2.2926: Vim9: no good error for using :legacy in a :def function

Problem:    Vim9: no good error for using :legacy in a :def function.
Solution:   Give an explicit error where :legacy is not working.
            (closes #8309)

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2926,
 /**/
     2925,
 /**/