patch 8.2.3504: Vim9: warning for signed vs unsigned

Problem:    Vim9: warning for signed vs unsigned.
Solution:   Add type cast.
diff --git a/src/version.c b/src/version.c
index 1be4d54..978e012 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3504,
+/**/
     3503,
 /**/
     3502,