In the latest version of the frontent-shared package, `extraRoute` has a
mandatory property `group` that must be either
`"home" | "foundations" | "patterns" | "components"`;

There are three ways to fix this:

* make the `group` property optional in the frontend-shared package (I
  don't know if that's a good idea).

* cast the `string` type to the one of the allowed types: `    group:
  /** @type {'components'} */ ('components'),`

* cast the `extraRoute` (this PR).