PostgreSQL backups marked as "success" when storage is full

If there isn't enough storage to create a PostgreSQL backup, the message "Successfully backed up..." is displayed even though the backup size is `0`.

```
Backing up 'patroni-master:5432/foo' to '/backups/daily/2024-09-25/patroni-master-foo_2024-09-25_01-06-13.sql.gz.in_progress' ...
pg_dump: error: could not write to output file: No space left on device
gzip: stdout: No space left on device
Successfully backed up patroni-master:5432/foo.
Backup written to /backups/daily/2024-09-25/patroni-master-foo_2024-09-25_01-06-13.sql.gz.
Database Size: 4070 MB
Backup Size: 0
```