resource/aws_athena_workgroup: Ensure we check tags attribute setting error
resource/aws_athena_workgroup: Ensure we check tags attribute setting error

Output from acceptance testing:

```
--- PASS: TestAccAWSAthenaWorkGroup_disappears (10.58s)
--- PASS: TestAccAWSAthenaWorkGroup_basic (14.71s)
--- PASS: TestAccAWSAthenaWorkGroup_Configuration_ResultConfiguration_EncryptionConfiguration_SseS3 (14.98s)
--- PASS: TestAccAWSAthenaWorkGroup_Description (22.34s)
--- PASS: TestAccAWSAthenaWorkGroup_Configuration_PublishCloudWatchMetricsEnabled (22.90s)
--- PASS: TestAccAWSAthenaWorkGroup_Configuration_BytesScannedCutoffPerQuery (22.92s)
--- PASS: TestAccAWSAthenaWorkGroup_Configuration_EnforceWorkgroupConfiguration (23.13s)
--- PASS: TestAccAWSAthenaWorkGroup_State (32.09s)
--- PASS: TestAccAWSAthenaWorkGroup_Tags (32.27s)
--- PASS: TestAccAWSAthenaWorkGroup_Configuration_ResultConfiguration_EncryptionConfiguration_Kms (54.86s)
--- PASS: TestAccAWSAthenaWorkGroup_Configuration_ResultConfiguration_OutputLocation (54.90s)
```

kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws