Migrate backported StrEnum to built-in StrEnum (#97101)

homeassistant/components/event/__init__.py

@@ -3,10 +3,10 @@ from __future__ import annotations
 
 from dataclasses import asdict, dataclass
 from datetime import datetime, timedelta
+from enum import StrEnum
 import logging
 from typing import Any, Self, final
 
-from homeassistant.backports.enum import StrEnum
 from homeassistant.config_entries import ConfigEntry
 from homeassistant.core import HomeAssistant
 from homeassistant.helpers.config_validation import (  # noqa: F401