Fix race condition in AccountSettingsHandler local echo (#9172)

Should fix https://github.com/vector-im/element-web/issues/23006

src/settings/handlers/AccountSettingsHandler.ts

@@ -165,8 +165,8 @@ export default class AccountSettingsHandler extends MatrixClientBackedSettingsHa
 
         content[field] = value;
 
-        await this.client.setAccountData(eventType, content);
-
+        // Attach a deferred *before* setting the account data to ensure we catch any requests
+        // which race between different lines.
         const deferred = defer<void>();
         const handler = (event: MatrixEvent) => {
             if (event.getType() !== eventType || event.getContent()[field] !== value) return;
@@ -175,6 +175,8 @@ export default class AccountSettingsHandler extends MatrixClientBackedSettingsHa
         };
         this.client.on(ClientEvent.AccountData, handler);
 
+        await this.client.setAccountData(eventType, content);
+
         await deferred.promise;
     }