[TRI-2755] v3 run log outputs with empty array inside objects aren't shown

[matt-aitken]

This task:

export const myTask = task({
  id: 'some-id',
  run: async () => {
    return {
      hooks: [],
    };
});

Has the correct output:

{
  "hooks": [],
}

But in the log data/on the run page is shows just an empty object. This is a bug with the flattenAttributes/unflattenAttributes code we use with our OpenTelemetry pipeline.

_TRI-2755