GroundControl can easily block iOS beta versions from your devices. This will prevent your users from installing the special profile that enables prerelease versions.
In GroundControl, add the “Set Restrictions” action to your workflow, and check “Disable manual config profile installs.” A similar option should be available in your MDM, if you prefer over-the-air management. Now users won’t be able to install the Apple profile that enables beta software updates.