Bug 1442712 - Re-enable about_studies tests r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D5285

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

toolkit/components/normandy/test/browser/browser.ini

@@ -7,7 +7,6 @@ head = head.js
 # Skip this test when FHR/Telemetry aren't available.
 skip-if = !healthreport || !telemetry
 [browser_about_studies.js]
-skip-if = true # bug 1442712
 [browser_actions_AddonStudyAction.js]
 [browser_actions_ConsoleLogAction.js]
 [browser_actions_PreferenceRolloutAction.js]

toolkit/components/normandy/test/browser/browser_about_studies.js

@@ -15,7 +15,8 @@ return async (...args) => (
 decorate_task(
   withAboutStudies,
   async function testAboutStudiesWorks(browser) {
-    ok(browser.contentDocumentAsCPOW.getElementById("app"), "App element was found");
+    const appFound = await ContentTask.spawn(browser, null, () => content.document.getElementById("app"));
+    ok(appFound, "App element was found");
   }
 );