vim-patch:9.2.0605: tests: Test_screenpos() is flaky in GUI (#40156)

Problem:  Test_screenpos() fails intermittently in the GUI testgui CI
          job with "Expected {'row': 22} but got {'row': 23}".  In the
          GUI, the window height reported by getwininfo() before the
          final redraw can be stale, so the cached wininfo.height does
          not match the actual window height when the assertion runs.
Solution: Use winheight(winid) at assertion time so the height reflects
          the window state after the redraw.

closes: vim/vim#20457

https://github.com/vim/vim/commit/781a91ac54fc7e647a0d2d85df9a4b884fb28ee8

Co-authored-by: thinca <thinca@gmail.com>

test/old/testdir/test_cursor_func.vim

@@ -125,7 +125,7 @@ func Test_screenpos()
   exe "normal G\<C-Y>\<C-Y>"
   redraw
   let winbar_height = get(wininfo, 'winbar', 0)
-  call assert_equal({'row': winrow + wininfo.height - 1 + winbar_height,
+  call assert_equal({'row': winrow + winheight(winid) - 1 + winbar_height,
 	\ 'col': wincol + 7,
 	\ 'curscol': wincol + 7,
 	\ 'endcol': wincol + 7}, winid->screenpos(line('$'), 8))