Bump version to 7.2.0.pre to avoid backup version mismatches, fixes #7375

#### What does this MR do?

This PR updates the version to `7.2.0.pre` to avoid backup migration problems.

#### Why was this MR needed?

Currently it's possible to migrate an old 7.1 backup to the current development version because of same version. Since these versions have different database schemas, this leads to errors.