address review comments

src/panels/lovelace/components/notifications/hui-notifications-button.ts

@@ -60,7 +60,7 @@ class HuiNotificationsButton extends LitElement {
 
   private _clicked() {
     this.opened = true;
-    fireEvent(this, "opened", { value: this.opened });
+    fireEvent(this, "opened-changed", { value: this.opened });
   }
 }
 

src/panels/lovelace/hui-root.ts

@@ -194,7 +194,7 @@ class HUIRoot extends LitElement {
                   <hui-notifications-button
                     .hass="${this.hass}"
                     .opened="${this._notificationsOpen}"
-                    @opened="${this._handleNotificationsOpenChanged}"
+                    @opened-changed="${this._handleNotificationsOpenChanged}"
                     .notifications="${this._notifications}"
                   ></hui-notifications-button>
                   <ha-start-voice-button