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_tabpage.vim b/src/testdir/test_tabpage.vim
index 60a5f3d..e222067 100644
--- a/src/testdir/test_tabpage.vim
+++ b/src/testdir/test_tabpage.vim
@@ -555,7 +555,7 @@
 
 func Test_tabpage_cmdheight()
   if !CanRunVimInTerminal()
-    throw 'Skipped: only works with terminal'
+    throw 'Skipped: cannot make screendumps'
   endif
   call writefile([
         \ 'set laststatus=2',