Removal of collections results in foreign key violations from the maintenance thread.

[WillemElbers]

2022-10-21 07:23:08,617 ERROR [org.hibernate.engine.jdbc.spi.SqlExceptionHelper#logExceptions:142] - Cannot delete or update a parent row: a foreign key constraint fails (`vcr`.`resource`, CONSTRAINT `FKEBABC40E8E3FCDB` FOREIGN KEY (`vc_id`) REFERENCES `virtualcollection` (`id`))
2022-10-21 07:23:08,617 INFO [org.hibernate.engine.jdbc.batch.internal.AbstractBatchImpl#release:208] - HHH000010: On release of batch it still contained JDBC statements
2022-10-21 07:23:08,620 ERROR [eu.clarin.cmdi.virtualcollectionregistry.VirtualCollectionRegistryMaintenanceImpl#perform:78] - unexpected error while doing maintenance
javax.persistence.RollbackException: Error while committing the transaction
	at org.hibernate.internal.ExceptionConverterImpl.convertCommitException(ExceptionConverterImpl.java:81) ~[hibernate-core-5.4.24.Final.jar:5.4.24.Final]
	at org.hibernate.engine.transaction.internal.TransactionImpl.commit(TransactionImpl.java:104) ~[hibernate-core-5.4.24.Final.jar:5.4.24.Final]
	at eu.clarin.cmdi.virtualcollectionregistry.VirtualCollectionRegistryMaintenanceImpl.purgeDeletedCollections(VirtualCollectionRegistryMaintenanceImpl.java:207) ~[classes/:?]
	at eu.clarin.cmdi.virtualcollectionregistry.VirtualCollectionRegistryMaintenanceImpl.perform(VirtualCollectionRegistryMaintenanceImpl.java:75) ~[classes/:?]
	at eu.clarin.cmdi.virtualcollectionregistry.VirtualCollectionRegistryImpl$1.run(VirtualCollectionRegistryImpl.java:96) ~[classes/:?]
...