[css-values-3][editorial] set wpt open by default, as the spec is close to REC so seeing at a glance where the fails are is valuable

Author: svgeesus

css-values-3/Overview.bs

@@ -17,6 +17,7 @@ Ignored Terms: <spacing-limit>, pairing, property
 Ignored Vars: Cn+1, n
 Inline Github Issues: no
 Default Highlight: css
+WPT Display: open
 </pre>
 <pre class='link-defaults'>
 spec: css-backgrounds-3; type: type; text: <position>