HTML and latex generation are not checked by dune build @install

[emillon]

In #3406, some blocks look like this:

```sh skip
>>> (ls .)
Could not find matching handler: ls
```

This triggers (and should) an error in mdx, but this only happens in @html, not in @runtest. As a result, it's missed by ocaml-ci which runs @install for monorepo builds. As a workaround, this alias (or @site? what about @latex?) can be added to @install.

[yminsky]

I'm surely missing something, but what's wrong with the listed block? Why should it error out at all?