Prevent new versions from being uploaded with the same semver as a previously deleted version

[budak7273]

There have been multiple occasions on which mod developers delete a version upload to fix something and then upload a new version with the same semver. They end up with different version uuids on the backend, but this breaks the Mod Manager for all users who got a copy of the deleted version in the mean time, since it only cares about mod version semvers. We can avoid this issue (and help enforce proper versioning) by ensuring that new uploads can't share a semver with deleted mod versions.