Use latest tag on minio after fix

Context: https://gitlab.com/gitlab-org/gitlab/-/issues/341209#note_691545285

I believe this is now fixed in the latest minio image, and we can unpin the version in gitlab-qa if we want.

While looking into this today I saw that several minio issues were logged for version RELEASE.2021-09-18T18-09-59Z where users were having uploads stop working with varying errors. While there wasn't a clear cause for our bucket not found issue here. Users reported problems were fixed by the minio release on the 23rd.

I reran gitlab-qa Test::Instance::Image gitlab/gitlab-ce:nightly --omnibus-config object_storage -- --tag object_storage locally with minio latest and am getting all tests passing