Fix the incorrect retrieval query in return_tasks function

[ozer550]

Summary

• Fix the incomplete query for fetching the TaskResult and CustomTaskMetadata in return tasks.

Manual verification steps performed

1. Trigger a task other than apply_channel_changes, apply_user_changes.
2. Sync does not crash now and returns tasks correctly.

Does this introduce any tech-debt items?

As there is no foreign key relation between the TaskResult and CustomTaskMetadata models the retrieval for both of them takes more than 2 queries fetching and filtering the same object.

References

closes #4323

Contributor's Checklist

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Reviewer's Checklist

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• Automated test coverage is satisfactory
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