As of VirtualBox 6.1.28, host-only networks are restricted to
`192.168.56.0/21` by default, so spinning up the Vagrant boxes with
secondary networks fail with an error `E_ACCESSDENIED`.

Update the IP configuration of the Vagrant boxes to fall within the
allowed range so that we don't need to ask developers from the
community to make VirtualBox configuration updates outside of their
normal Vagrant use.