tests/resource/aws_eks_node_group: Update TestAccAWSEksNodeGroup_ReleaseVersion argument value (#12172)
tests/resource/aws_eks_node_group: Update TestAccAWSEksNodeGroup_ReleaseVersion argument value (#12172)

Reference: https://github.com/awslabs/amazon-eks-ami/issues/423
Reference: https://github.com/aws/containers-roadmap/issues/771

There is currently no lookup mechanism for these values other than the website. See referenced issue for hopeful path forward via a new SSM Parameter, although there does appear to be a delay between the AMI release and EKS API support.

Previous output from acceptance testing (master and latest version testing):

```
--- FAIL: TestAccAWSEksNodeGroup_ReleaseVersion (1225.88s)
    testing.go:654: Step 0 error: errors during apply:

        Error: error creating EKS Node Group (tf-acc-test-9113909416381506697:tf-acc-test-9113909416381506697): InvalidParameterException: Requested Node Group release version 1.14.7-20190927 is invalid. Allowed release version is 1.14.8-20191213

--- FAIL: TestAccAWSEksNodeGroup_ReleaseVersion (1375.87s)
    testing.go:654: Step 0 error: errors during apply:

        Error: error creating EKS Node Group (tf-acc-test-7174874914828901519:tf-acc-test-7174874914828901519): InvalidParameterException: Requested Node Group release version 1.14.9-20200122 is invalid. Allowed release version is 1.14.8-20191213
```

Output from acceptance testing:

```
--- PASS: TestAccAWSEksNodeGroup_ReleaseVersion (1564.18s)
```
kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws