Enable IETF QUIC RFCv1 version

RFC 9000 has shipped! https://www.rfc-editor.org/rfc/rfc9000.html

We see a small but non-zero amount of traffic for this version on go/quic-versions, and it hasn't caused any issues.

PiperOrigin-RevId: 376258250
diff --git a/quic/core/quic_flags_list.h b/quic/core/quic_flags_list.h
index 487d7ce..a9d9e9d 100644
--- a/quic/core/quic_flags_list.h
+++ b/quic/core/quic_flags_list.h
@@ -78,7 +78,7 @@
 // If true, drop unsent PATH_RESPONSEs and rely on peer\'s retry.
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_drop_unsent_path_response, true)
 // If true, enable QUIC version h3 (RFCv1).
-QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_enable_version_rfcv1, false)
+QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_enable_version_rfcv1, true)
 // If true, enable server retransmittable on wire PING.
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_enable_server_on_wire_ping, true)
 // If true, include stream information in idle timeout connection close detail.