patch 8.2.4304: Vim9: slice() makes a copy but doesn't change the type

Problem:    Vim9: slice() makes a copy but doesn't change the type.
Solution:   Change the declared type like copy(). (closes #9696)

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4304,
 /**/
     4303,
 /**/