ci: fix curl_helpers.hpp include path in three hook tests

Three test files included curl_helpers.hpp via the repo-rooted path
"test/integ/curl_helpers.hpp", but the build's -I list only adds
"-I../../test" (the test source dir) — there is no -I./. that would
resolve the leading "test/" component. The build fails with "No
such file or directory" on every lane that actually builds tests.

Switch to "./curl_helpers.hpp", matching the convention used by every
other test in test/integ/ (e.g. authentication.cpp's
#include "./test_utils.hpp").

Author: etr

test/integ/hooks_body_chunk_observes_progress.cpp

@@ -29,7 +29,7 @@
 
 #include "./httpserver.hpp"
 #include "./littletest.hpp"
-#include "test/integ/curl_helpers.hpp"
+#include "./curl_helpers.hpp"
 
 using httpserver::body_chunk_ctx;
 using httpserver::create_webserver;

test/integ/hooks_body_chunk_short_circuit_no_leak.cpp

@@ -28,7 +28,7 @@
 
 #include "./httpserver.hpp"
 #include "./littletest.hpp"
-#include "test/integ/curl_helpers.hpp"
+#include "./curl_helpers.hpp"
 
 using httpserver::body_chunk_ctx;
 using httpserver::create_webserver;

test/integ/hooks_request_received_short_circuit.cpp

@@ -29,7 +29,7 @@
 
 #include "./httpserver.hpp"
 #include "./littletest.hpp"
-#include "test/integ/curl_helpers.hpp"
+#include "./curl_helpers.hpp"
 
 using httpserver::body_chunk_ctx;
 using httpserver::create_webserver;