HTTP ToStr: ToStrError { _priv: () } (failed to convert header to a str)

This happens with `https://www-cdn.anthropic.com/872c653b2d0501d6ab44cf87f43e1dc4853e4d37.pdf`, most likely because of the `Content-Disposition` that has non-ASCII: `’` (`e28099`). It *is* technically invalid but shouldn't break `epoxy-server`.