Add missing type hints to websocket_api (#50915)

homeassistant/components/websocket_api/permissions.py

@@ -2,6 +2,10 @@
 
 Separate file to avoid circular imports.
 """
+from __future__ import annotations
+
+from typing import Final
+
 from homeassistant.components.frontend import EVENT_PANELS_UPDATED
 from homeassistant.components.lovelace.const import EVENT_LOVELACE_UPDATED
 from homeassistant.components.persistent_notification import (
@@ -22,7 +26,7 @@ from homeassistant.helpers.entity_registry import EVENT_ENTITY_REGISTRY_UPDATED
 
 # These are events that do not contain any sensitive data
 # Except for state_changed, which is handled accordingly.
-SUBSCRIBE_ALLOWLIST = {
+SUBSCRIBE_ALLOWLIST: Final[set[str]] = {
     EVENT_AREA_REGISTRY_UPDATED,
     EVENT_COMPONENT_LOADED,
     EVENT_CORE_CONFIG_UPDATE,