set arn attribute from DB subnet group response instead of arn endpoint

[saravanan30erd]

Output from acceptance testing:

$ make testacc TEST=./aws/ TESTARGS='-run=TestAccAWSDBSubnetGroup_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws/ -v -run=TestAccAWSDBSubnetGroup_basic -timeout 120m
=== RUN   TestAccAWSDBSubnetGroup_basic
--- PASS: TestAccAWSDBSubnetGroup_basic (90.97s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	91.000s
...

[bflad]

LGTM, thanks @saravanan30erd! 🚀

=== RUN   TestAccAWSDBSubnetGroup_namePrefix
--- PASS: TestAccAWSDBSubnetGroup_namePrefix (11.70s)
=== RUN   TestAccAWSDBSubnetGroup_generatedName
--- PASS: TestAccAWSDBSubnetGroup_generatedName (11.87s)
=== RUN   TestAccAWSDBSubnetGroup_withUndocumentedCharacters
--- PASS: TestAccAWSDBSubnetGroup_withUndocumentedCharacters (12.26s)
=== RUN   TestAccAWSDBSubnetGroup_basic
--- PASS: TestAccAWSDBSubnetGroup_basic (13.41s)
=== RUN   TestAccAWSDBSubnetGroup_importBasic
--- PASS: TestAccAWSDBSubnetGroup_importBasic (14.10s)
=== RUN   TestAccAWSDBSubnetGroup_updateDescription
--- PASS: TestAccAWSDBSubnetGroup_updateDescription (18.47s)

[bflad]

This has been released in version 1.27.0 of the AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!