patch 8.2.4533: Vim9: no test that after assigning null type is still checked

Problem:    Vim9: no test that after assigning null the type is still checked.
Solution:   Add a test.
diff --git a/src/version.c b/src/version.c
index 9248ca4..9b72517 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4533,
+/**/
     4532,
 /**/
     4531,