Throws errors if scope["method"] is missing

[simonw]

I got this error:

  File "../site-packages/asgi_csrf.py", line 98, in app_wrapped_with_csrf
    if scope["method"] in {"GET", "HEAD", "OPTIONS", "TRACE"}:
KeyError: 'method'
ERROR:    Application startup failed. Exiting.

[simonw]

I think this is due to the ASGI lifespan protocol. This will help test it: https://github.com/simonw/til/blob/main/asgi/lifespan-test-httpx.md