Set correct parent span in async environment

[antonpirker]

How do you use Sentry?

Sentry Saas (sentry.io)

Version

1.9.10

Steps to Reproduce

• Have a FastAPI app
• Have a FastAPI middleware like this one: https://github.com/getsentry/demo-app-django-react/blob/main/backend/fastapi/main.py#L80-L101
• Do something in this middleware that creates a span (like the redis call in the span
• Reload an endpoint that uses this middleware
• Go to the "Performance" section of sentry.io and look at the event
• You will see this:
  

Expected Result

The redis span should be under the CounterMiddleware.

Actual Result

The redis span is under the AsyncExitStackMiddleware

[antonpirker]

This is also related with this amazing issue: #1187

[sl0thentr0py]

and #772

[sl0thentr0py]

also #772 (comment)

[sl0thentr0py]

and #1333 (comment)