Add asgiref to EXTERNAL_REQ_ALLOWLIST

[huynguyengl99]

Hi, is it ok to add asgiref package to the EXTERNAL_REQ_ALLOWLIST.

As I mentioned in the PR typeshed-internal/stub_uploader#173, the package is in the PyPI top 1000 list (ranked 195th). It is fully type-hinted and under the Django umbrella, so I think it’s safe to add to the EXTERNAL_REQ_ALLOWLIST.