Ensuring the `web` generator is properly covered in the CI

[avivkeller]

Currently, we test the web generator by ensuring that Vercel can deploy it. However, in the event that this generator fails, Vercel will still deploy a website, just, well, not a very good one.

We can ensure that errors are properly bubbled back to us via:

1. Ensuring that Vercel fails when any generator fails
2. Adding the web generator to our CI matrix