patch 8.2.4395: some code lines not covered by tests

Problem:    Some code lines not covered by tests.
Solution:   Add a few more test cases.  Fix getting more than one error for
            invalid assignment.
diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index 9c988c9..c4a457e 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -1359,7 +1359,8 @@
   v9.CheckDefFailure(['var null = 1'], 'E1034:')
   v9.CheckDefFailure(['var this = 1'], 'E1034:')
 
-  v9.CheckDefFailure(['[a; b; c] = g:list'], 'E452:')
+  v9.CheckDefFailure(['[a; b; c] = g:list'], 'E1001:')
+  v9.CheckDefFailure(['var [a; b; c] = g:list'], 'E1080:')
   v9.CheckDefExecFailure(['var a: number',
                        '[a] = test_null_list()'], 'E1093:')
   v9.CheckDefExecFailure(['var a: number',