🐛 fix event maybe converted when checking type (#876)

Fix: 修复 event 类型检查会对类型进行自动转换

tests/plugins/param/param_bot.py

@@ -1,5 +1,13 @@
 from nonebot.adapters import Bot
 
 
-async def get_bot(b: Bot):
+async def get_bot(b: Bot) -> Bot:
+    return b
+
+
+class SubBot(Bot):
+    ...
+
+
+async def sub_bot(b: SubBot) -> SubBot:
     return b