test(starlette): Refactor shared test parametrization

[szokeasaurusrex]

We use the same parametrization for testing FastAPI's and Starlette's failed_request_status_codes because the FastApiIntegration's constructor is the same as StarletteIntegration's constructor (the former is a subclass of the latter).

Here, we refactor the test cases to define the parametrization once, then use it in both tests. This change will make some future changes simpler, since we only need to change the parameters in one place to affect the test for both frameworks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.30%. Comparing base (7e4992a) to head (5c6c778).
Report is 3 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3562      +/-   ##
==========================================
- Coverage   84.31%   84.30%   -0.01%     
==========================================
  Files         133      133              
  Lines       13890    13890              
  Branches     2930     2930              
==========================================
- Hits        11711    11710       -1     
  Misses       1440     1440              
- Partials      739      740       +1     

see 1 file with indirect coverage changes