Update AMB schema and URL

[acka47]

Hi @nichtich, we have published the first official version of AMB, see https://dini-ag-kim.github.io/amb/latest/. Going through the remaining AMB issues, I stumbled over dini-ag-kim/amb#150 and had a look at the validation service.

I noticed two things:

1. The used draft schema seems to be cached by the application and the breaking change in dini-ag-kim/amb@d785187 isn't taken into account. Thus, valid resources do not validate correctly, see e.g. http://format.gbv.de/validate/validate?format=amb&data=&url=https%3A%2F%2Fgithub.com%2Fdini-ag-kim%2Famb%2Fraw%2Fmain%2F20231019%2Fexamples%2Fvalid%2FlearningResourceType.json
2. The schema URL needs to be updated. You could point to the latest schema by using https://dini-ag-kim.github.io/amb/latest/schemas/schema.json. I noticed that the service also supports versioning so you might also add that.

I tried to make a PR but the data apparently is not in the repo. Is there any way to provide a fix for such a problem by myself?