assignment is unnessary under suppress()

Maybe a bit of an edge case, but this code gives warning of unnessary assignments:
```
t = "<>"
with suppress(AttributeError):
# Set to type arg.
t = cls = get_args(self.__orig_class__)[0]
# If a class, set to the qualname.
t = cls.__qualname__
```

It should probably recognise that any code in a `suppress()` block may not actually run to completion.

https://lgtm.com/projects/g/aio-libs/aiohttp/snapshot/d6d827d7b26f2a54999f8a150ef230fe627aa435/files/aiohttp/helpers.py?sort=name&dir=ASC&mode=heatmap#x6cb8804f71fae0f2:1

首先在 aiohttp/helpers.py 中的範例上重現不必要的指派警告，重點關注 Python 的 suppress() 內容管理器周圍的指派分析行為。檢查相關的 CodeQL 查詢及其測試，然後驗證當執行可能無法完成時，suppress() 區塊內的指派不再被回報。

由索引模型根據 Issue 內容生成。