Fixed trusted_cidr_blocks variable when empty

[yutachaos]

Description

• Error occured when trusted_cidr_blocks is empty

╷
│ Error: "" is not a valid CIDR block: invalid CIDR address:
│
│   with module.example_ecs_cluster.aws_security_group_rule.ingress,
│   on .terraform/modules/example_ecs_cluster/security_group.tf line 17, in resource "aws_security_group_rule" "ingress":
│   17:   cidr_blocks       = local.trusted_cidr_blocks
│
╵

sample code

module "example_ecs_cluster" {
  source       = "github.com/jetbrains-infra/terraform-aws-ecs-cluster?ref=v0.5.4" // see https://github.com/jetbrains-infra/terraform-aws-ecs-cluster/releases
  cluster_name = "FooBar"

  // subnets where the ECS nodes are hosted
  subnets_ids = [
    aws_subnet.private_subnet_1.id,
    aws_subnet.private_subnet_2.id
  ]
}