hcltest: update a remaining stale reference to "zcl"
hcltest: update a remaining stale reference to "zcl"

hashicorp/hcl,hashicorp/hcl,strivecast/hcl,strivecast/hcl,hashicorp/hcl,hashicorp/hcl,hashicorp/hcl,strivecast/hcl,strivecast/hcl,strivecast/hcl