patch 8.2.4728: no test that v:event cannot be modified

Problem:    No test that v:event cannot be modified.
Solution:   Add a test. (closes #10139)
diff --git a/src/version.c b/src/version.c
index ff5f399..9657184 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4728,
+/**/
     4727,
 /**/
     4726,