Old Python version in Vagrant

[KalobTaulien]

Vagrant is using Python 3.6 which isn't supported by Wagtail 2.16 and Django 4. I think config.vm.box = "torchbox/wagtail-stretch64" in Vagrantfile needs to be updated, but I'm unsure how to update the VM Box.

This issue doesn't allow Vagrant users to use bakerydemo with Vagrant.