cors-preflight-not-cors-safelisted.any.js fails because of HeaderValue implementation

[ghostd]

As commented in the code:

servo/components/script/dom/headers.rs

Lines 358 to 363 in c661cc8

	// https://fetch.spec.whatg.org/#concept-header-value just says not to have
	// newlines, nulls, or leading/trailing whitespace. It even allows
	// octets that aren't a valid UTF-8 encoding, and WPT tests reflect this.
	// The HeaderValue class does not fully reflect this, so headers
	// containing bytes with values 1..31 or 127 can't be created, failing
	// WPT tests but probably not affecting anything important on the real Internet.

The current implementation of HeaderValue does not allow "non printable" byte as header value. I open this issue to discuss and have a history of a potential decision.

[pshaughn]

A corresponding upstream issue is at hyperium/http#376