patch 8.2.1179: Test_termwinscroll() sometimes hangs in the GUI

Problem:    Test_termwinscroll() sometimes hangs in the GUI.
Solution:   Skip the test in the GUI.
diff --git a/src/testdir/test_terminal2.vim b/src/testdir/test_terminal2.vim
index d89b975..c1b38d2 100644
--- a/src/testdir/test_terminal2.vim
+++ b/src/testdir/test_terminal2.vim
@@ -184,6 +184,8 @@
 
 func Test_termwinscroll()
   CheckUnix
+  " TODO: Somehow this test sometimes hangs in the GUI
+  CheckNotGui
 
   " Let the terminal output more than 'termwinscroll' lines, some at the start
   " will be dropped.