patch 8.2.1011: Vim9: some code not tested

Problem:    Vim9: some code not tested.
Solution:   Add a few more test cases.  Reorder checks for clearer error.
            Remove unreachable code.
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index e0776b5..224f4fd 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -524,6 +524,7 @@
 			g:anint)
   assert_equal(9, g:alsoint + 5)
   assert_equal(14, g:alsoint + g:anint)
+  assert_equal([1, 2, 3, 4], [1] + g:alist)
 
   assert_equal(54, 60 - 6)
   assert_equal(50, 60 -