Return an error if asked to update a package that does not exist

When attempting to update a major version and violating the version constraints in `gleam.toml` the CLI does not throw an error, as it does when attempting to do the same with `gleam add`

Example:

```sh
$ gleam update gleam_httpc@5
  Resolving versions

The following dependencies have new major versions available:

gleam_httpc 4.1.1 -> 5.0.0
```

gleam v1.12.0