fix(core): refine HttpError.status property type

[iuioiua]

As this is property only ever has an error HTTP status code (>400).

[marvinhagemeister]

The assumption that only an instance of HttpError is thrown is not correct. There is no guarantee for that, see:

app.use(() => {
  throw "foo"
});

[iuioiua]

Ah, yes 🤦🏾‍♂️ I did at least assume that an Error is thrown.

[iuioiua]

Gentle ping @marvinhagemeister

[marvinhagemeister]

LGTM