fix: typo in exception message for ImproperlyConfiguredException #4445

Job	Run time
slotscheck	17s
mypy	54s
pyright	34s
Test server integration (uvicorn<0.27.0)	37s
Test Minimal Application with Base Dependencies	14s
Test server integration (uvicorn>=0.27.0)	37s
Test Minimal Pydantic 1 application	14s
test-platform-compat	0s
validate	15s
test (3.10) / test	1m 38s
test (3.12) / test	3m 3s
test (3.11) / test	1m 57s
test (3.8) / test	2m 48s
test (3.9) / test	1m 47s
build-docs	2m 22s
codeql	2m 9s
upload-test-coverage	19s
sonar	0s
	19m 45s

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