Cleanup db directory after tests

[quentinlesceller]

Required for Windows CI to pass otherwise it will fail with:

cleaning output dir failed - Os { code: 2, kind: NotFound, message: "The system cannot find the file specified." }
thread 'test_block_building_max_weight' panicked at 'called `Result::unwrap()` on an `Err` value: Error::Code(112, 'There is not enough space on the disk.

EDIT: This does not seems to fix the issue encountered.
EDIT 2: Seems to work now.