patch 8.2.1355: Vim9: no error using :let for options and registers

Problem:    Vim9: no error using :let for options and registers.
Solution:   Give an error. (closes #6568)
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index b96411f..5ed9a3d 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -463,13 +463,16 @@
                             '[x, y; z] = [1]'], 'E1093:')
 
   call CheckDefFailure(['let somevar'], "E1022:")
-  call CheckDefFailure(['let &option'], 'E1052:')
+  call CheckDefFailure(['let &tabstop = 4'], 'E1052:')
   call CheckDefFailure(['&g:option = 5'], 'E113:')
+  call CheckScriptFailure(['vim9script', 'let &tabstop = 4'], 'E1052:')
 
   call CheckDefFailure(['let $VAR = 5'], 'E1016: Cannot declare an environment variable:')
+  call CheckScriptFailure(['vim9script', 'let $ENV = "xxx"'], 'E1016:')
 
   call CheckDefFailure(['let @~ = 5'], 'E354:')
   call CheckDefFailure(['let @a = 5'], 'E1066:')
+  call CheckScriptFailure(['vim9script', 'let @a = "abc"'], 'E1066:')
 
   call CheckDefFailure(['let g:var = 5'], 'E1016: Cannot declare a global variable:')
   call CheckDefFailure(['let w:var = 5'], 'E1016: Cannot declare a window variable:')