Use the right SetFlag() function in TlsClientHandshakerTest

This blocks rolling quiche to Chromium as compiling caused the following errors:
- error: no member named 'SetFlag' in namespace 'absl'
- error: use of undeclared identifier 'FLAGS_gfe2_reloadable_flag_quic_gfe_allow_alps_new_codepoint'

PiperOrigin-RevId: 587934731

quiche/quic/core/tls_client_handshaker_test.cc

diff --git a/quiche/quic/core/tls_client_handshaker_test.cc b/quiche/quic/core/tls_client_handshaker_test.cc
index 35c0328..c6b0e77 100644
--- a/quiche/quic/core/tls_client_handshaker_test.cc
+++ b/quiche/quic/core/tls_client_handshaker_test.cc
@@ -887,8 +887,8 @@
     SCOPED_TRACE(absl::StrCat("Test allows alps new codepoint:",
                               server_allow_alps_new_codepoint));
     crypto_config_->set_alps_use_new_codepoint(true);
-    absl::SetFlag(&FLAGS_gfe2_reloadable_flag_quic_gfe_allow_alps_new_codepoint,
-                  server_allow_alps_new_codepoint);
+    SetQuicReloadableFlag(quic_gfe_allow_alps_new_codepoint,
+                          server_allow_alps_new_codepoint);
     CreateConnection();
 
     // Add a DoS callback on the server, to test that the client sent the new