patch 8.1.1953: more functions can be used as a method

Problem:    More functions can be used as a method.
Solution:   Allow more functions to be used as a method.
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 961f274..557687b 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -565,7 +565,7 @@
   set rtp+=./sautest
   lockvar g:footest#x
   unlockvar g:footest#x
-  call assert_equal(-1, islocked('g:footest#x'))
+  call assert_equal(-1, 'g:footest#x'->islocked())
   call assert_equal(0, exists('g:footest#x'))
   call assert_equal(1, g:footest#x)
   let &rtp = old_rtp