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_highlight.vim b/src/testdir/test_highlight.vim
index 4548457..78dbead 100644
--- a/src/testdir/test_highlight.vim
+++ b/src/testdir/test_highlight.vim
@@ -533,7 +533,7 @@
 
 func Test_cursorline_after_yank()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
 
   call writefile([
@@ -555,7 +555,7 @@
 
 func Test_cursorline_with_visualmode()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
 
   call writefile([
@@ -575,7 +575,7 @@
 
 func Test_wincolor()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
 
   call writefile([