Bug 1885279 - Fix timing issue in messageDisplayAction API. r=mkmelin

I am not 100% sure why this is popping up now, but it is not a recent
regression, but a real bug. The code in question was introduced in Bug 1803255.

We are currently not awaiting the call to `super.updateWindow()`.

This patch adds the same mechanism which is already used in
`ExtensionToolbarButtons.sys.mjs`:

https://searchfox.org/comm-central/rev/a0bc09a88c7e060ba8cafb62a40dc0f36153d8d2/mail/components/extensions/ExtensionToolbarButtons.sys.mjs#647-653

Differential Revision: https://phabricator.services.mozilla.com/D204584

--HG--
extra : amend_source : 86945d83b709d56067be8295b0d08ee24fb49a3f

mail/components/extensions/parent/ext-messageDisplayAction.js

@@ -106,11 +106,13 @@ this.messageDisplayAction = class extends ToolbarButtonAPI {
    * Overrides the super class to update every about:message in this window.
    */
   async updateWindow(window) {
+    const promises = [];
     for (const bc of window.browsingContext.getAllBrowsingContextsInSubtree()) {
       if (bc.currentURI.spec == "about:message") {
-        super.updateWindow(bc.window);
+        promises.push(super.updateWindow(bc.window));
       }
     }
+    await Promise.all(promises);
   }
 
   /**