Workflow improvements (#9609)

* remove unnecessary download links

GitHub already shows them in a table right below it.

* detach `npm run style` from `npm run test`

* decouple lint from test in workflows

Which means that we don't need to do the crazy linking in certain
workflows.

* hoist the `CI` environment variable

* create dedicated `lint` job

The `lint` tests will run against source files and should not be
dependant on a specific node version. Instead of running the `npm run
style` on every node version we use, we can and should only run it once.

* remove `prettier-plugin-tailwindcss`

As long as we use older versions of node/npm where we can't have
ourselves as a dependency, it is a bit of a mess to maintain properly
sorted html in tests.

Let's remove it for now until we have a better solution!