OTEL_PYTHON_FASTAPI_EXCLUDED_URLS doesn't suppress child spans from being created

[bbeattie-phxlabs]

Consider the scenario:

• An environment in which opentelemetry-instrumentation-aiohttp-client and opentelemetry-instrumentation-fastapi are installed
• A FastAPI endpoint that makes a call via aiohttp
• This generates a span for the FastAPI endpoint and a span for the aiohttp call.

Now alter the environment such that OTEL_PYTHON_FASTAPI_EXCLUDED_URLS excludes the endpoint. Surprisingly, the aiohttp still generates a span!

I see conversation around open-telemetry/opentelemetry-specification#530 on the subject of "stop tracing at this point", but that issue has sat open for 3+ years now.

Is there a better way to tackle this?