patch 8.1.1840: Testing: WorkingClipboard() is not accurate

Problem:    Testing: WorkingClipboard() is not accurate.
Solution:   Check feature clipboard_working instead.
diff --git a/src/testdir/test_paste.vim b/src/testdir/test_paste.vim
index eab4cff..c30140f 100644
--- a/src/testdir/test_paste.vim
+++ b/src/testdir/test_paste.vim
@@ -70,9 +70,8 @@
 endfunc
 
 func Test_paste_clipboard()
-  if !WorkingClipboard()
-    return
-  endif
+  CheckFeature clipboard_working
+
   let @+ = "nasty\<Esc>:!ls\<CR>command"
   new
   exe "normal i\<C-R>+\<Esc>"