Astro v6 upgrade #36
Description
The blog broke silently when renovate updated it to v6. This is due to changes in the content collection API that were added in v5 and are now enforced in v6. A detailed guide for upgrading can be found here: https://docs.astro.build/en/guides/upgrade-to/v5/#legacy-v20-content-collections-api
As part of this we should add at least one visual regression test for the blog, so this won't happen again. #28 is a good candidate for this.