eventbridge-sfn-terraform: 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 events put-events --entries file://event-A.json --region us-east-1
{
    "FailedEntryCount": 0,
    "Entries": [
        {
            "EventId": "c50fee9c-1316-0d0d-b8e1-e53d12c1289f"
        }
    ]
}

$ aws events put-events --entries file://event-B.json --region us-east-1
{
    "FailedEntryCount": 0,
    "Entries": [
        {
            "EventId": "5369ae64-7800-6347-1b6a-7a36d89b6c2a"
        }
    ]
}

$ aws events put-events --entries file://event-Fail.json --region us-east-1
{
    "FailedEntryCount": 0,
    "Entries": [
        {
            "EventId": "9710a0b6-a0bc-1471-28d6-1324da7c5bf5"
        }
    ]
}

Thank you😀

---

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[kakakakakku]

note: Fix to correct service name😀
https://docs.aws.amazon.com/step-functions/latest/dg/welcome.html