[BUG]: github_organization_custom_properties of type `true_false` detects drift on `default_value` indefinitely

### Expected Behavior

With following configuration planned and applied.
```
resource "github_organization_custom_properties" "foo" {
property_name = "foo"
value_type = "true_false"
required = true

default_value = "true"
}
```

any additional plan results in no drift detected.

### Actual Behavior

An additional plan will result in following drift:

```
Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
~ update in-place

Terraform will perform the following actions:

# github_organization_custom_properties.stedisentry_enabled will be updated in-place
~ resource "github_organization_custom_properties" "foo" {
+ default_value = "true"
id = "foo"
# (6 unchanged attributes hidden)
}

Plan: 0 to add, 1 to change, 0 to destroy.
```

### Terraform Version

Terraform: `1.15.7`
GitHub provider: `6.12.1`

### GitHub Installation Type

- [x] GitHub.com (Free, Pro, or Team)
- [ ] GitHub Enterprise Server (on-premises)
- [ ] GitHub Enterprise Cloud with Personal Accounts (github.com)
- [ ] GitHub Enterprise Cloud with Managed Users/EMU (github.com)
- [ ] GitHub Enterprise Cloud with Data Residency (*.ghe.com)
- [ ] I don't know

### Affected Resource(s)

- github_organization_custom_properties

### Terraform Configuration Files

```hcl
resource "github_organization_custom_properties" "foo" {
property_name = "foo"
value_type = "true_false"
required = true

default_value = "true"
}
```

### Steps to Reproduce

_No response_

### Debug Output

```shell

```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Start with the github_organization_custom_properties resource and reproduce the configuration in the issue using Terraform 1.15.7 and provider 6.12.1. Compare the state after apply with the next plan for a true_false property; done means default_value="true" no longer appears as an in-place drift.

Written by the indexing model from the issue text.