fix(test): ignore curl exit code when sending a large header

[JackMyers001]

When running the tests locally on my workstation, the "Make request with a header exceeding limit" test fails because curl exits with a non-zero exit code (56) after attempting to send a too-large header. I'm running curl version 8.20.0.

We can simply ignore this exit code and continue, and the tests pass without issue.

For reference, the full curl log I'm seeing is:

---------------------------------------------------------------
 Make request with a header exceeding limit.
---------------------------------------------------------------
* Host localhost:8443 was resolved.
* IPv6: ::1
* IPv4: 127.0.0.1
*   Trying [::1]:8443...
* ALPN: curl offers h2,http/1.1
} [5 bytes data]
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
} [1564 bytes data]
* SSL Trust: peer verification disabled
{ [5 bytes data]
* TLSv1.3 (IN), TLS handshake, Server hello (2):
{ [1210 bytes data]
* TLSv1.3 (IN), TLS change cipher, Change cipher spec (1):
{ [1 bytes data]
* TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
{ [21 bytes data]
* TLSv1.3 (IN), TLS handshake, Certificate (11):
{ [1503 bytes data]
* TLSv1.3 (IN), TLS handshake, CERT verify (15):
{ [520 bytes data]
* TLSv1.3 (IN), TLS handshake, Finished (20):
{ [52 bytes data]
* TLSv1.3 (OUT), TLS change cipher, Change cipher spec (1):
} [1 bytes data]
* TLSv1.3 (OUT), TLS handshake, Finished (20):
} [52 bytes data]
* SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384 / X25519MLKEM768 / RSASSA-PSS
* ALPN: server accepted http/1.1
* Server certificate:
*   subject: C=GB; ST=London; L=London; O=Mendhak; CN=my.example.com
*   start date: Jun 14 08:54:47 2026 GMT
*   expire date: Jun 11 08:54:47 2036 GMT
*   issuer: C=GB; ST=London; L=London; O=Mendhak; CN=my.example.com
*   Certificate level 0: Public key type RSA (4096/152 Bits/secBits), signed using sha256WithRSAEncryption
* OpenSSL verify result: 12
*  SSL certificate verification failed, continuing anyway!
* Established connection to localhost (::1 port 8443) from ::1 port 38066
  % Total    % Received % Xferd  Average Speed  Time    Time    Time   Current
                                 Dload  Upload  Total   Spent   Left   Speed
  0      0   0      0   0      0      0      0                              0* using HTTP/1.x
} [5 bytes data]
> GET / HTTP/1.1
> Host: localhost:8443
> User-Agent: curl/8.20.0
> Accept: */*
> Large-Header: <snip>
>
* Request completely sent off
{ [5 bytes data]
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
{ [265 bytes data]
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
{ [265 bytes data]
< HTTP/1.1 431 Request Header Fields Too Large
< Connection: close
<
} [5 bytes data]
* TLSv1.3 (OUT), TLS alert, decode error (562):
} [2 bytes data]
* OpenSSL SSL_read: OpenSSL/3.6.3: error:0A000126:SSL routines::unexpected eof while reading, errno 0

* closing connection #0
curl: (56) OpenSSL SSL_read: OpenSSL/3.6.3: error:0A000126:SSL routines::unexpected eof while reading, errno 0

[mendhak]

Thanks for the PRs. I did some testing and I see the change was introduced in curl 8.9.0 so this looks like a good approach. I can still see the header being returned in the response.