patch 8.1.1483: skipped tests are not properly listed

Problem:    Skipped tests are not properly listed.
Solution:   Throw a "Skipped" exception instead of using ":finish" or ":return".
diff --git a/src/testdir/test_timers.vim b/src/testdir/test_timers.vim
index e900b1f..963cc23 100644
--- a/src/testdir/test_timers.vim
+++ b/src/testdir/test_timers.vim
@@ -281,7 +281,7 @@
 
 func Test_restore_count()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot run Vim in a terminal window'
   endif
   " Check that v:count is saved and restored, not changed by a timer.
   call writefile([