Ignore unknown fields in push V2 json

[bemusementpark]

This PR fixes an issue where push notifications were not showing the message content in the notification drawer.

Invalid push notification
    kotlinx.serialization.json.internal.JsonDecodingException: Unexpected JSON token at offset 137: Encountered an unknown key 't' at path: $.n
    Use 'ignoreUnknownKeys = true' in 'Json {}' builder to ignore unknown keys.
    JSON input: {"@": "...", "#": "...", "n": 0, "t": ..., "z": ..., "l": ...}
    at kotlinx.serialization.json.internal.JsonExceptionsKt.JsonDecodingException(JsonExceptions.kt:24)