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_quotestar.vim b/src/testdir/test_quotestar.vim
index d21ab35..432862e 100644
--- a/src/testdir/test_quotestar.vim
+++ b/src/testdir/test_quotestar.vim
@@ -1,11 +1,9 @@
 " *-register (quotestar) tests
 
 source shared.vim
-if !WorkingClipboard()
-  throw 'Skipped: no working clipboard'
-endif
+source check.vim
 
-source shared.vim
+CheckFeature clipboard_working
 
 func Do_test_quotestar_for_macunix()
   if empty(exepath('pbcopy')) || empty(exepath('pbpaste'))