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_popup.vim b/src/testdir/test_popup.vim
index 538dd22..edb0399 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -735,7 +735,7 @@
 
 func Test_popup_and_previewwindow_dump()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
   call writefile([
     \ 'set previewheight=9',
@@ -797,7 +797,7 @@
 
 func Test_popup_position()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
   call writefile([
 	\ '123456789_123456789_123456789_a',
@@ -839,7 +839,7 @@
 
 func Test_popup_command()
   if !CanRunVimInTerminal() || !has('menu')
-    return
+    throw 'Skipped: cannot make screendumps and/or menu feature missing'
   endif
 
   call writefile([