Bug 1593445 - enable document channel pref in coop wpt for beta simulation, r=valentin

Differential Revision: https://phabricator.services.mozilla.com/D52399

--HG--
extra : moz-landing-system : lando

testing/web-platform/meta/html/cross-origin-opener-policy/__dir__.ini

@@ -1,4 +1,4 @@
-prefs: [browser.tabs.remote.useCrossOriginOpenerPolicy:true, browser.tabs.remote.useCrossOriginEmbedderPolicy:true]
+prefs: [browser.tabs.remote.useCrossOriginOpenerPolicy:true, browser.tabs.remote.useCrossOriginEmbedderPolicy:true, browser.tabs.documentchannel:true]
 disabled:
   if os == "android": no content process switch in android
 leak-threshold: [tab:102400]