changing project environment variables after the resource has been created fails

    error: Error updating project: Could not upsert environment variables for project prj_....., unexpected error: bad_request - Invalid request: should be object.

while the api docs say it's possible to create "one or more" if you look at the payload it accepts a single object and not an array

https://github.com/vercel/terraform-provider-vercel/blob/main/vercel/resource_project.go#L493