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)
diff --git a/src/version.c b/src/version.c
index f86aa89..3df4cfc 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4304,
+/**/
     4303,
 /**/
     4302,