tests: fix http2 tests to use CRLF headers

tests: fix http2 tests to use CRLF headers

Prior to this change some tests that rely on nghttpx proxy did not use
CRLF headers everywhere. A recent change in nghttp2, which updated its
version of llhttp (HTTP parser), requires curl's HTTP/1.1 test server to
use CRLF headers.

Ref: https://github.com/nghttp2/nghttp2/commit/9d389e8

Fixes https://github.com/curl/curl/issues/9364
Closes https://github.com/curl/curl/pull/9365