patch 8.2.4286: Vim9: strict type checking after copy() and deepcopy()

Problem:    Vim9: strict type checking after copy() and deepcopy().
Solution:   Allow type to change after making a copy. (closes #9644)
diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index e3606d8..73b3310 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -484,7 +484,7 @@
           ->copy()
           ->copy()
   END
-  v9.CheckDefFailure(lines, 'E1012:', 2)
+  v9.CheckDefExecFailure(lines, 'E1012:', 4)
 
   lines =<< trim END
       var x: any