patch 8.2.4311: Vim9: changing script variable type not caught compile time

Problem:    Vim9: changing script variable type not caught at compile time.
Solution:   Set the declared type.
diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index 79c08d3..7d3e2c1 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -692,6 +692,16 @@
   END
   v9.CheckDefExecAndScriptFailure(lines, 'E1013: Argument 2: type mismatch, expected list<number> but got list<string>', 4)
   unlet g:myList
+
+  lines =<< trim END
+      vim9script
+      var lds = [1, 2, 3]
+      def Func()
+          echo lds->extend(['x'])
+      enddef
+      defcompile
+  END
+  v9.CheckScriptFailure(lines, 'E1013:')
 enddef
 
 def Test_extend_dict()