fix bug with 4xx check

[DeanWay]

The status_code_key is set to uppercase above, leading to this check always being false.
This invalidated the expected behaviour of a specified 4xx or 4XX overriding the default 422 response

[codecov]

Codecov Report

Merging #547 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #547   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files         251    251           
  Lines        5988   5892   -96     
=====================================
- Hits         5988   5892   -96

Impacted Files	Coverage Δ
fastapi/openapi/utils.py	100% <100%> (ø)	⬆️
...est_additional_responses_custom_validationerror.py	100% <0%> (ø)	⬆️
docs/src/app_testing/tutorial003.py	100% <0%> (ø)	⬆️
...t_query_params_str_validations/test_tutorial001.py	100% <0%> (ø)	⬆️
tests/test_custom_swagger_ui_redirect.py	100% <0%> (ø)	⬆️
docs/src/first_steps/tutorial001.py	100% <0%> (ø)	⬆️
tests/test_additional_responses_router.py	100% <0%> (ø)	⬆️
docs/src/application_configuration/tutorial001.py	100% <0%> (ø)	⬆️
tests/test_duplicate_models_openapi.py	100% <0%> (ø)	⬆️
tests/test_serialize_response_dataclass.py	100% <0%> (ø)	⬆️
... and 61 more

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[DeanWay]

Just noticed #517. Either works, only difference here is moving the erroneous check away from using a string literal

[tiangolo]

Thanks @DeanWay ! I just merged #517 , so, this should be solved in the next release.

But thanks for your contribution! 🍰