http: handle both "h2" and "h2h3" in curl info lines

http: handle both "h2" and "h2h3" in curl info lines

When redacting auth tokens in trace output from curl, we look for http/2
headers of the form "h2h3 [header: value]". This comes from b637a41ebe
(http: redact curl h2h3 headers in info, 2022-11-11).

But the "h2h3" prefix changed to just "h2" in curl's fc2f1e547 (http2:
support HTTP/2 to forward proxies, non-tunneling, 2023-04-14). That's in
released version curl 8.1.0; linking against that version means we'll
fail to correctly redact the trace. Our t5559.17 notices and fails.

We can fix this by matching either prefix, which should handle both old
and new versions.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>