[BUG] : Foreign Key Constraint fails OCEs syncing process

[alinauroz]

Describe the bug
When an OCE is generated via a CoBudget bucket, and subsequently, that bucket is deleted, issue arise during the synchronisation of OCEs for the corresponding round. This issues trigger foreign key constraint violations, because bucket is missing, resulting in synchronisation failures.

To Reproduce
Steps to reproduce the behavior:

1. Create an OpenCollective Expense (OCE) via the Bucket
2. Delete the Cobudget Bucket
3. Sync OCEs for the Round through Round's Integration Settings
4. See the Foreign Key Constraint Failure

Expected behaviour
Syncing process should not fail. The bucketId in OCE which are missing in Cobudget database should be removed.