patch 8.2.3690: Vim9: "filter #pat# cmd" does not work

Problem:    Vim9: "filter #pat# cmd" does not work.
Solution:   Do not see #pat# as a comment.

src/testdir/test_vim9_cmd.vim

@@ -714,6 +714,16 @@ def Test_command_modifier_filter()
       assert_match('very specific z3d37dh234 string', Screenline(&lines))
   END
   CheckDefAndScriptSuccess(lines)
+
+  lines =<< trim END
+      edit foobar
+      redir => g:filter_out
+      filter #foobar# ls
+      redir END
+      assert_match('"foobar"', g:filter_out)
+      unlet g:filter_out
+  END
+  CheckDefAndScriptSuccess(lines)
 enddef
 
 def Test_win_command_modifiers()