patch 8.2.4495: help test fails in 24 line terminal

Problem:    Help test fails in 24 line terminal.
Solution:   Use up to 23 lines for text.
diff --git a/src/testdir/test_help.vim b/src/testdir/test_help.vim
index b8b9bbc..5c46de4 100644
--- a/src/testdir/test_help.vim
+++ b/src/testdir/test_help.vim
@@ -152,7 +152,7 @@
 
 " Test for setting the 'helpheight' option in the help window
 func Test_help_window_height()
-  let &cmdheight = &lines - 24
+  let &cmdheight = &lines - 23
   set helpheight=10
   help
   set helpheight=14