If a user used `append_dedupe`, they get the error:
```
{
"type": "LOG",
"log": {
"level": "FATAL",
"message": "1 validation error for ConnectorSpecification\nsupported_destination_sync_modes -> 2\n value is not a valid enumeration member; permitted: 'append', 'overwrite', 'append_dedup' (type=type_error.enum; enum_values=[<DestinationSyncMode.append: 'append'>, <DestinationSyncMode.overwrite: 'overwrite'>, <DestinationSyncMode.append_dedup: 'append_dedup'>])..."
}
}
```
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