patch 8.2.3332: Vim9: cannot assign to range in list

Problem:    Vim9: cannot assign to range in list.
Solution:   Implement overwriting a list range.
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 90f5679..1e7c812 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -164,11 +164,14 @@
 
 " test for range assign
 func Test_list_range_assign()
-  let l = [0]
-  let l[:] = [1, 2]
-  call assert_equal([1, 2], l)
-  let l[-4:-1] = [5, 6]
-  call assert_equal([5, 6], l)
+  let lines =<< trim END
+      VAR l = [0]
+      LET l[:] = [1, 2]
+      call assert_equal([1, 2], l)
+      LET l[-4 : -1] = [5, 6]
+      call assert_equal([5, 6], l)
+  END
+  call CheckLegacyAndVim9Success(lines)
 endfunc
 
 " Test removing items in list