Fix race condition in S3 delete expired tests

[Murderlon]

Regularly seeing a race condition occurring when two CI runs happen around the same time, which happens often if you have multiple PRs or a PR and a new commit in main.

Details: https://github.com/tus/tus-node-server/actions/runs/7206763772/job/19632235153

[fenos]

Yes, this is a tricky one to fix, since they both try to call s3.deleteExpired() resulting in deleting each other files and the assertion then fails.

maybe we can create a new bucket with a random name during the tests and delete it right after