patch 8.2.2609: test disabled on MS-Windows even though it should work

Problem:    Test disabled on MS-Windows even though it should work.
Solution:   Restore the condition for skipping the test. (Ken Takata,
            closes #7970)
diff --git a/src/testdir/test_startup.vim b/src/testdir/test_startup.vim
index e8be191..169c213 100644
--- a/src/testdir/test_startup.vim
+++ b/src/testdir/test_startup.vim
@@ -109,7 +109,9 @@
 endfunc
 
 func Test_help_arg()
-  CheckNotMSWindows
+  if !has('unix') && has('gui_running')
+    throw 'Skipped: does not work with gvim on MS-Windows'
+  endif
 
   if RunVim([], [], '--help >Xtestout')
     let lines = readfile('Xtestout')