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.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4533,
 /**/
     4532,
 /**/