Turn off "Expect" header in test

Without this explicitly set, curl might decide to add a
`Expect: 100-continue` header if it deems the request too large.
See also: https://gms.tf/when-curl-sends-100-continue.html

ext/curl/tests/curl_postfields_array.phpt

@@ -31,6 +31,7 @@ $options = [
 	CURLOPT_FORBID_REUSE => 1,
 	CURLOPT_TIMEOUT => 1,
 	CURLOPT_POSTFIELDS => $fields,
+	CURLOPT_HTTPHEADER => [ 'Expect:' ],
 ];
 
 $ch = curl_init();