Fix FastAPI/Starlette middleware with positional arguments.

[antonpirker]

Fixes #3246

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.59%. Comparing base (8672dc1) to head (63b25d9).

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
sentry_sdk/integrations/starlette.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4118      +/-   ##
==========================================
+ Coverage   79.56%   79.59%   +0.02%     
==========================================
  Files         140      140              
  Lines       15581    15581              
  Branches     2643     2643              
==========================================
+ Hits        12397    12401       +4     
+ Misses       2345     2343       -2     
+ Partials      839      837       -2     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/starlette.py	84.09% <66.66%> (ø)

... and 3 files with indirect coverage changes