Switch vagrant to use Debian 12

[tomhughes]

Similar to #5157 this switches the vagrant configuration to use Debian 12 instead of Ubuntu.

Only tested with the libvirt provider at the moment.

[nenad-vujicic]

Wouldn't be safer to stick to specific Debian version (e.g. 12.7) instead of using the latest v12? Similarly for #5157

[tomhughes]

I don't know enough about Debian to be able to answer that but the minor versions are just updated installers that include the latest updates aren't they?

[tomhughes]

As far as I can tell there aren't any images for specific releases anyway - the list just contains one image for each major version which looks like it is regularly updated with the latest packages.

[mmd-osm]

Test completed with status "ok" on VirtualBox 6.1 w/ virtualbox provider:

Finished in 449.210410s, 4.0671 runs/s, 2230.1976 assertions/s.
1827 runs, 1001828 assertions, 0 failures, 0 errors, 0 skips
Coverage report generated for Minitest, Minitest-0, Minitest-1 to /srv/openstreetmap-website/coverage. 6287 / 6679 LOC (94.13%) covered.
Lcov style coverage report generated for Minitest, Minitest-0, Minitest-1 to coverage/lcov.info