patch 8.2.3333: Vim9: not enough tests run with Vim9

Problem:    Vim9: not enough tests run with Vim9.
Solution:   Run a few more tests in Vim9 script and :def function.
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 1e7c812..f904872 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -457,6 +457,19 @@
   endfunc
   let expected = 'a:' . string(get(d, 'func'))
   call assert_equal(expected, d.func(string(remove(d, 'func'))))
+
+  " similar, in a way it also works in Vim9
+  let lines =<< trim END
+      VAR d = {1: 1, 2: 'x'}
+      func GetArg(a)
+        return "a:" .. a:a
+      endfunc
+      LET d.func = function('GetArg')
+      VAR expected = 'a:' .. string(get(d, 'func'))
+      call assert_equal(expected, d.func(string(remove(d, 'func'))))
+  END
+  call CheckTransLegacySuccess(lines)
+  call CheckTransVim9Success(lines)
 endfunc
 
 func Test_dict_literal_keys()