Bug 1905895 - Fix intermittent comm/mail/test/browser/message-reader/browser_convertToEventOrTask.js | index 0 must exist to be clicked on. r=tobyp

Don't close the window before the copy had finished.

100% green try build: https://treeherder.mozilla.org/jobs?repo=try-comm-central&revision=7670d96177bdab00163b8f65bb37be0d915441f2

Differential Revision: https://phabricator.services.mozilla.com/D224065

--HG--
extra : rebase_source : 34724e2615f7501dcdb29311d974f047b40b3508
extra : amend_source : f7bab5f3516dfc01c99ffb185d31809f54705429

mail/test/browser/message-reader/browser_convertToEventOrTask.js

@@ -69,6 +69,10 @@ add_task(async function test_convertToEvent() {
       { label: "ConvertToEvent" },
     ]
   );
+  await TestUtils.waitForCondition(
+    () => folder.getTotalMessages(false) == 1,
+    "waiting for copy to folder to complete"
+  );
   await BrowserTestUtils.closeWindow(msgc);
 
   const msg = await select_click_row(0);