Return HTTP 400 when attempting to post an event with an unregistered schema #3198

Job	Run time
build (ubuntu-latest, 3.8)	11s
check_release	17s
build (ubuntu-latest, 3.11)	10s
integration_check (ubuntu-latest, 3.8)	13s
Check Links	11s
build (windows-latest, 3.8)	13s
integration_check (ubuntu-latest, 3.9)	10s
integration_check_pypy	11s
build (windows-latest, 3.11)	10s
integration_check (ubuntu-latest, 3.10)	10s
integration_check (ubuntu-latest, 3.11)	16s
build (macos-latest, 3.8)	12s
Make SDist	15s
build (macos-latest, 3.11)	13s
Test Docs	12s
build (windows-latest, 3.9)	11s
Test Examples	16s
Test Lint	16s
build (ubuntu-latest, pypy-3.8)	10s
Test Minimum Versions	18s
build (macos-latest, 3.10)	13s
Test Prereleases	8s
build (ubuntu-latest, 3.12)	12s
Install from SDist and Test	1s
coverage	1s
tests_check	2s
	4m 52s

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