Update to Zola 0.22.1

[LawnGnome]

Per the discussion in #1796, this PR updates the blog to use Zola 0.22. As part of that, the text syntax has been removed, and the built-in light-plus and dark-plus syntax highlighting themes are now used.

The snapshot test diffs here are going to look horrific, but spot checking a few blog pages in practice reveals only a couple of apparent differences:

1. The light mode no longer highlights Rust type names with a colour, and
2. The dark mode now highlights quotes with the same colour as the actual string literal within the quotes.

The second change actually slightly improves the WCAG contrast scores. The first one makes no effective difference, although I personally miss the colour.

I obviously have no way to test the GitHub action changes, so we'll just have to see what happens. It works locally if I recreate the steps in a rust:1.91.1 Docker container. 🤷

Rendered

[senekor]

The themes don't actually seem to work yet.

[LawnGnome]

The themes don't actually seem to work yet.

Interesting. What are you seeing? (Or not seeing.)

[senekor]

Just regular, unhighlighted, "black on white" text.