Bug 1901764 - Make select label not react to events. r=dholbert, a=dmeehan

This is the same fix as bug 1893177, but for the <label>. It should
ideally not be necessary at all, but it's unclear to me why the target
difference makes us not see the pointer-up event.

That's worth digging into, and will file a follow-up on it, but this
restores the previous behavior exactly, so should be worth doing in the
interim while we figure that out.

Differential Revision: https://phabricator.services.mozilla.com/D214709

layout/style/res/forms.css

@@ -284,6 +284,7 @@ select > button {
 select > label {
   display: inline-block;
   overflow: clip;
+  pointer-events: none;
   cursor: unset;
 }