[BUG]: `github_codespaces_organization_secret` gets lost from state and recreated after secret value change

### Expected Behavior

`github_codespaces_organization_secret` should behave consistently across consecutive tofu plan runs — showing "No changes" when neither the HCL nor the remote resource has changed. Drift behavior should match `github_actions_organization_secret` (detect metadata drift, ignore value drift since the API doesn't return values).

### Actual Behavior

The resource disappears from state during refresh, causing the next plan to show + create instead of "No changes." The pattern is reproducible:

tofu apply — creates the secret successfully
tofu plan — "No changes" ✓
tofu plan (after a change of secret value in UI) — wants to + creates the secret again

This does NOT happen with `github_actions_organization_secret` or `github_dependabot_organization_secret` in the same configuration, same provider version, same auth method.

### Terraform Version

OpenTofu v1.10.6
on darwin_arm64
+ provider registry.opentofu.org/integrations/github v6.11.1

### Affected Resource(s)

`github_codespaces_organization_secret`

### Terraform Configuration Files

```hcl
resource "github_codespaces_organization_secret" "poc_1" {
secret_name = "POC_CODESPACES_SECRET"
plaintext_value = "Testval"
visibility = "private"
}
```

### Steps to Reproduce

1. `tofu apply` — secret is created
2. `tofu plan` — shows "No changes"
3. Change `POC_CODESPACES_SECRET` value in UI
4. `tofu plan` again — shows:

```
# github_codespaces_organization_secret.poc_1[0] will be created
+ resource "github_codespaces_organization_secret" "poc_1" {
+ created_at = (known after apply)
+ id = (known after apply)
+ plaintext_value = (sensitive value)
+ secret_name = "POC_CODESPACES_SECRET"
+ updated_at = (known after apply)
+ visibility = "private"
}

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

5. tofu apply — re-creates the secret
Cycle repeats from step 2

Expected cause:
`github_actions_organization_secret` received a drift detection rework in PR #3069 (by @stevehipwell), adding remote_updated_at, CustomizeDiff with diffSecret, and StateUpgraders. This fix was not applied to `github_codespaces_organization_secret`, which likely still uses the old pattern where a timestamp mismatch during Read causes the resource to be removed from state instead of triggering an in-place update.
`github_dependabot_organization_secret` does not exhibit this behavior in my testing — it may have received the fix or uses a different Read implementation.

References:
PR #3069 — fix: Correct secret drift implementation (Actions secrets)

### Debug Output

```shell

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### Panic Output

```shell

```

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