[`airflow`] Add missing `AIR302` attribute check (#17115)
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## Summary
<!-- What's the purpose of the change? What does it do, and why? -->
attribute check was missing in the previous implementation
e.g.
```python
from airflow.api.auth.backend import basic_auth
basic_auth.auth_current_user
```
This PR adds this kind of check.
## Test Plan
<!-- How was it tested? -->
The test case has been added to the button of the existing test
fixtures, confirmed to be correct and later reorgnaized
