Update Terraform version at `required_version`

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Package ecosystem

Terraform

### Package manager version

Terraform

### Language version

Terraform

### Manifest location and content before the Dependabot update

Any Terraform file with the following block:
```terraform
terraform {
required_providers {
aws = {
version = "~> 2.13.0"
}
random = {
version = ">= 2.1.2"
}
}

required_version = "~> 0.12.29"
}
```

https://developer.hashicorp.com/terraform/tutorials/configuration-language/versions

### dependabot.yml content

Default `dependabot.yml` to update Terraform.

```yaml
version: 2
updates:
- package-ecosystem: "terraform"
directory: "/"
schedule:
interval: "daily"
```

### Updated dependency

Main Terraform version.

### What you expected to see, versus what you actually saw

Actually, `dependabot` does not update the Terraform version at `required_version`.

Maybe this is an expected behaviour, if not I can give it a go and try to add the code to do it.

Looking into the code at https://github.com/dependabot/dependabot-core/blob/389cb8a49af6a4c499da6322a6c138f734ccc310/terraform/lib/dependabot/terraform/file_parser.rb#L58-L67 we should fetch the `required_version` object.

### Native package manager behavior

_No response_

### Images of the diff or a link to the PR, issue, or logs

_No response_

### Smallest manifest that reproduces the issue

_No response_

Start in terraform/lib/dependabot/terraform/file_parser.rb, especially lines 58-67, and read the linked Terraform version-constraint documentation. Trace how required_providers constraints are fetched and determine how required_version should be handled. Done means Dependabot updates the Terraform version constraint in matching Terraform files without disrupting provider constraints.

Written by the indexing model from the issue text.