src/transformers/models/groupvit/modeling_groupvit.py/GroupViTStage/concat_x
class GroupViTStage:    def concat_x(self, x: torch.Tensor, group_token: Optional[torch.Tensor] = None) -> torch.Tensor:
        if group_token is None:
            return x
        return torch.cat([x, group_token], dim=1)