fix(asgi): Fix KeyError if transaction does not exist

[kevinji]

When "transaction" does not exist on the event, it will raise KeyError: "transaction". Ensure that this code handles "transaction" and "transaction_info" gracefully.

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[sentrivana]

Hey @kevinji, thank you for the contribution!

Added a suggestion, please take a look.

Also, can you tell me when you observe this KeyError? What's your setup like? Wondering what cases there are where there is no transaction on the event and if that's not something we should fix.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.55%. Comparing base (189e4a9) to head (1a1c628).
Report is 2 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4095   +/-   ##
=======================================
  Coverage   79.55%   79.55%           
=======================================
  Files         140      140           
  Lines       15521    15523    +2     
  Branches     2631     2631           
=======================================
+ Hits        12347    12349    +2     
  Misses       2338     2338           
  Partials      836      836           

Files with missing lines	Coverage Δ
sentry_sdk/integrations/asgi.py	85.81% <100.00%> (+0.20%)	⬆️

... and 2 files with indirect coverage changes

[kevinji]

We have a Starlette app which is running into this exception when fastapi_integrations is set to True.

[sentrivana]

Thanks for reworking, two more small suggestions and then we are good to merge