Tilegarden runtime version is out of support

[KlaasH]

The Tilegarden lambda function is using the Node 12 runtime, which has been deprecated for quite a while and out of support since spring 2023.

That's fine as long as it keeps chugging along without requiring any attention, which is what it has been doing for ~4 years, but Lambda won't let you deploy Node 12 functions anymore, so if something should happen that would require that we change or replace it, we would have to upgrade it to a supported runtime (currently Node 18 or 20) before we would be able to deploy.

Probably if we do replace it as preventative maintenance (as opposed to in an emergency) we should create a new function with a new name, to avoid any risk of breaking the old one until we're sure the new one is good to go.