The localdev cluster won't start up on VirtualBox 6.1.28

I set up my new laptop with NixOS 21.11. When I tried to start the localdev cluster, VirtualBox / Vagrant yelled at me:

The IP address configured for the host-only network is not within the
allowed ranges. Please update the address used to be within the allowed
ranges and run the command again.

  Address: 192.168.67.21
  Ranges: 192.168.56.0/21

Valid ranges can be modified in the /etc/vbox/networks.conf file. For
more information including valid format see:

  https://www.virtualbox.org/manual/ch06.html#network_hostonly

I'm not clear on whether this is a consequence of having a newer version of VirtualBox but https://www.virtualbox.org/manual/ch15.html#idp6189968 does say:

Network: More administrative control over host-only network ranges to prevent trouble due to misconfiguration, see Section 6.7, “Host-Only Networking”. Check updated documentation or your VMs may stop working!

This is a bit vague but maybe it is related.

The host-only networking documentation does say VirtualBox wants one to use 192.168.56.0/21 though. I don't remember if there was a reason we're using 192.168.67.x instead.