Gardening: mark two tests to get WebKit Linux (deps) green

fast/forms/number/number-appearance-spinbutton-disabled-readonly.html
fast/forms/select/listbox-appearance-basic.html

These two fail consistently on this bot only, not the WebKit Linux ToT bot.

BUG=353736
TEST=
TBR=zmo@chromium.org

Review URL: https://codereview.chromium.org/203443006

git-svn-id: svn://svn.chromium.org/blink/trunk@169480 bbb929c8-8fbe-4397-9dbb-9b2b20218538