Robustify the scrolling in the Help app test

This keeps failing on the accessibility section, and looking at
the screenshots I realized why. When you press 'down', GNOME
doesn't just 'snap' to the new view, it does a smooth downward
scroll. We're often matching *while it's scrolling*, so the
needle match is right at the bottom of the screen. But then the
animation continues, so when we get to the click action (even
though we use click_lastmatch it's not *instant* in openQA),
the thing we're trying to click (the "Accessibility" section
title) is a bit further up the screen, and the click 'misses'.

So, we need to wait out the scroll then re-assert and click.
This unfortunately will make the test take about 30 seconds
longer, but I don't see another way to do it. We could maybe
shave the wait_still_screen to one second...

Signed-off-by: Adam Williamson <awilliam@redhat.com>

tests/applications/help/help.pm

@@ -10,7 +10,12 @@ use utils;
 sub visit_section {
     my $section = shift;
     send_key_until_needlematch("help_section_$section", "down", 40, 1);
-    click_lastmatch();
+    # we have to wait then re-assert, because the down movement is
+    # animated, so we may match while it's still animating and then
+    # when the animation is complete the section title may be in a
+    # different place to where we first saw it
+    wait_still_screen 2;
+    assert_and_click("help_section_$section");
     assert_screen("help_section_content_$section");
     assert_and_click("help_breadcrumbs_home");
     assert_screen("help_main_screen");