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_balloon.vim b/src/testdir/test_balloon.vim
index 37fc57e..abf7d69 100644
--- a/src/testdir/test_balloon.vim
+++ b/src/testdir/test_balloon.vim
@@ -9,7 +9,7 @@
 
 source screendump.vim
 if !CanRunVimInTerminal()
-  throw 'Skipped: cannot run Vim in a terminal window'
+  throw 'Skipped: cannot make screendumps'
 endif
 
 let s:common_script =<< [CODE]