Ensure that 2.6.0 was implemented correctly

[Pakisan]

Known open specifications to check compatibility with:

• [x] anyof-asyncapi.yml
• [x] application-headers-asyncapi.yml
• [x] correlation-id-asyncapi.yml
• [x] gitter-streaming-asyncapi.yml
• [x] mercure-asyncapi.yml
• [x] not-asyncapi.yml
• [x] oneof-asyncapi.yml
• [x] operation-security-asyncapi.yml
• [x] rpc-client-asyncapi.yml
• [x] rpc-server-asyncapi.yml
• [x] simple.yml
• [x] slack-rtm-asyncapi.yml
• [x] streetlights-kafka.yml
• [x] streetlights-mqtt.yml
• [x] streetlights-operation-security.yml
• [x] websocket-gemini.yml

[Pakisan]

Close this issue after - https://github.com/asyncapi/jasyncapi/issues/126