patch 8.2.2980: popup window test is a bit flaky

Problem:    Popup window test is a bit flaky.
Solution:   Add a redraw command.
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index faadfe2..147a3a4 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -1552,6 +1552,7 @@
   call assert_equal(9, getcurpos()[2])
   call feedkeys('0', 'xt')
   call assert_equal('0', g:ignored)
+  redraw
   call assert_equal(1, getcurpos()[2])
 
   " x closes the popup