Bug 1562844 - Use correct tabId in Raptor r=robwu,rwood

More info: https://bugzilla.mozilla.org/show_bug.cgi?id=1562844#c9

Differential Revision: https://phabricator.services.mozilla.com/D41768

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

testing/raptor/webext/raptor/runner.js

@@ -456,7 +456,8 @@ async function nextCycle() {
         postToControlServer("status", `update tab: ${testTabID}`);
 
         // update the test page - browse to our test URL
-        ext.tabs.update(testTabID, { url: testURL }, testTabUpdated);
+        // "null" = active tab
+        ext.tabs.update(testTabID || null, { url: testURL }, testTabUpdated);
 
         if (testType == TEST_SCENARIO) {
           scenarioTimer();