Ensure that 3.0.0 was implemented correctly

[Pakisan]

Check that I didn't lost any changes done, in specification schema, after 04.10.2023

Known open specifications to check compatibility with:

• adeo-kafka-request-reply-asyncapi.yml
• anyof-asyncapi.yml
• application-headers-asyncapi.yml
• correlation-id-asyncapi.yml
• gitter-streaming-asyncapi.yml
• kraken-websocket-request-reply-message-filter-in-reply-asyncapi.yml
• kraken-websocket-request-reply-multiple-channels-asyncapi.yml
• mercure-asyncapi.yml
• not-asyncapi.yml
• oneof-asyncapi.yml
• operation-security-asyncapi.yml
• rpc-client-asyncapi.yml
• rpc-server-asyncapi.yml
• simple-asyncapi.yml
• slack-rtm-asyncapi.yml
• streetlights-kafka-asyncapi.yml
• streetlights-mqtt-asyncapi.yml
• streetlights-operation-security-asyncapi.yml
• websocket-gemini-asyncapi.yml

[Pakisan]

adeo-kafka-request-reply-asyncapi.yml is blocked by asyncapi/spec#1031

[Pakisan]

Similar issues with Schema:

example usage instead of examples

• Unable to parse a spec with an example attribute #163

Unknown property nullable

• Unable to parse a spec with an nullable attribute #164