Passing List to IAM Group Policy Template file

Question

I am creating policy based on tags. The environment value differs for each resource, so I have to add them as multiple values. Unable to pass as list. Tried join,split and for loop. None of them works. Pls help. Below code just add the value as "beta,test" which will not work as expected

main.tf

locals{
    workspaceValues = terraform.workspace == "dev" ? ["alpha", "dev"] : terraform.workspace == "test" ? ["beta", "test"] : ["prod", "staging"]
}

resource "aws_iam_group_policy" "inline_policy" {
  name   = "${terraform.workspace}_policy"
  group  = aws_iam_group.backend_admin.name
  policy = templatefile("policy.tpl", { env = join(",", local.workspaceValues), region = "${data.aws_region.current.name}", account_id = "${data.aws_caller_identity.current.account_id}" })
}

policy.tpl:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "ec2:*",
            "Resource": "*",
            "Condition": {
                "ForAllValues:StringLikeIfExists": {
                    "aws:ResourceTag/Environment": "${env}"
                }
            }
        }
    ]
}