New parser rule: refuse HTTP requests where a header field value
contains characters that
a) should never appear there in the first place,
b) might have lead to incorrect treatment in a proxy in front, and
c) might lead to unintended behaviour in applications.

From RFC 9110 section 5.5:
"Field values containing CR, LF, or NUL characters are invalid and
dangerous, due to the varying ways that implementations might parse
and interpret those characters; a recipient of CR, LF, or NUL within
a field value MUST either reject the message or replace each of those
characters with SP before further processing or forwarding of that
message."