Http Connectivity Grid Prevent Double H2 Scheduled

Fixed a bug in the HTTP connection pool grid where, when starting with HTTP/2 (e.g., HTTP/3 is disabled or broken) and the TCP connection fails, a redundant second TCP connection attempt was scheduled instead of immediately propagating the failure. This behavior can be temporarily reverted by setting the runtime flag envoy.reloadable_features.connectivity_grid_prevent_double_h2_scheduled to false.