ASGIStaticFilesHandler raises warning.

[Carlton Gibson]

#33735 added async support to StreamingHttpResponse for Django 4.2.

With Django 4.2rc1 and Daphne, ` raises a warning about the incorrect iterator type being used:

http/response.py:534: Warning: StreamingHttpResponse must consume synchronous iterators in order to serve them asynchronously. Use an asynchronous iterator instead.

This is because FileResponse is not async compatible (nor is that likely, since neither is open()).

A new project with:

INSTALLED_APPS = [
    "daphne",
    ...
]

ASGI_APPLICATION = "project.asgi.application"

runserver, and then visit any page serving static files such as /admin/.

The fix is to have ASGIStaticFilesHandler adapt the iterator in the same way StreamingHttpResponse does.