terraform-ecs-efs-integration: Update AWS Provider to v6

[kakakakakku]

Issue #, if available:
N/A

Description of changes:
Hi😀 Thanks for the useful patterns!

To keep this pattern maintainable, I updated the AWS Provider to v6.

Check

terraform apply completed successfully and works good.

$ aws ecs run-task \
    --cluster testing-serverlessland-efs-updater \
    --task-definition testing-serverlessland-efs-updater:1 \
    --network-configuration "awsvpcConfiguration={subnets=[subnet-xxxxxxxxxxxxxxxxx],securityGroups=[sg-xxxxxxxxxxxxxxxxx],assignPublicIp=DISABLED}" \
    --count 1 \
    --launch-type FARGATE \
    --region us-east-1

Thank you😀

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[kakakakakku]

note: CannotPullContainerError error occurred because IAM policy referenced wrong ECR repository ARN.

CannotPullContainerError: pull image manifest has been retried 1 time(s): failed to resolve ref 000000000000.dkr.ecr.us-east-1.amazonaws.com/testing-serverlessland-efs-updater:latest: unexpected status from HEAD request to https://000000000000.dkr.ecr.us-east-1.amazonaws.com/v2/testing-serverlessland-efs-updater/manifests/latest: 403 Forbidden