ASGI mounted to FastAPI mounts metrics to `/metrics/` instead of `/metrics`

The documentation gives an example application which mounts the ASGI app to /metrics in a FastAPI app

from fastapi import FastAPI
from prometheus_client import make_asgi_app

# Create app
app = FastAPI(debug=False)

# Add prometheus asgi middleware to route /metrics requests
metrics_app = make_asgi_app()
app.mount("/metrics", metrics_app)

and says that you should be able to see the metrics at http://localhost:8000/metrics, however if you try to access this endpoint

$ uvicorn app:app
INFO:     Started server process [1620866]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     127.0.0.1:34428 - "GET / HTTP/1.1" 404 Not Found
INFO:     127.0.0.1:34428 - "GET /favicon.ico HTTP/1.1" 404 Not Found
INFO:     127.0.0.1:34444 - "GET /metrics HTTP/1.1" 307 Temporary Redirect
INFO:     127.0.0.1:34444 - "GET /metrics/ HTTP/1.1" 200 OK

you get redirected to /metrics/.

It would be better if this redirect could be avoided.

Start with the FastAPI example in the linked documentation and reproduce the mounted /metrics request using uvicorn. Check whether the redirect is controlled by the documented client_python example or the FastAPI mount behavior; done means either avoiding the redirect or documenting the actual endpoint behavior clearly.