Disable prerelease text check in disk_guided_empty

This is causing all kinds of trouble, because when the test is
run on the Server DVD - with the 'orange to blue' gradient - the
prerelease note is dark red text on a dark blue background.
os-autoinst actually reduces the color depth of images/needles
and greyscales them before performing the match...but for this
dark red text on dark blue background, the result seems to be
that the text and background come out *the same grey*, so *any*
text will match the needle (even if it's completely different
text), as will *no text at all*. I've tried finessing around
this a few times but it just keeps happening, so for now I'm
just disabling the pre-release text check at this point. We still
have the check during _boot_to_anaconda, when the text appears
on a *grey* background and so isn't a problem. I'm not removing
the needles yet, until we hear back from upstream:

https://progress.opensuse.org/issues/56822

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

tests/disk_guided_empty.pm

@@ -22,7 +22,14 @@ sub run {
    my $branched = get_var('VERSION');
    if ($identification eq 'true' or $branched ne "Rawhide") {
        check_top_bar(); # See utils.pm
-       check_prerelease();
+       # disabled because we have issues with false needle matches
+       # on the pre-release note when it's dark red text on a dark
+       # blue background - os-autoinst greyscales images before
+       # comparing, and they wind up the same shade of grey, so we
+       # will get a 'match' for the pre-release needle even if the
+       # text is not there at all:
+       # https://progress.opensuse.org/issues/56822
+       # check_prerelease();
        check_version();
    }