[FEAT]: github_organization_custom_properties - support regex validation

### Describe the need

As of April 9th, 2025 [github_organization_custom_properties](https://registry.terraform.io/providers/integrations/github/latest/docs/resources/organization_custom_properties) now has support for [Regular Expression Matching](https://github.blog/changelog/2025-04-09-push-rule-delegated-bypass-and-custom-property-regex-support-are-generally-available-and-repository-policy-delegated-bypass-is-in-preview/#custom-properties-regular-expression-matching)

It's only possible for `Text` types, and is the suggested workaround for people who would use single/multi-select save for the limitation of 200 possible values in the list.

**For what it's worth** The schema has not been updated as of `GitHub-Api-Version 2026-03-10` so Data types as well as Resources won't have the ability to read the current values **but**

```bash
curl -L -X PUT \
-H "Accept: application/vnd.github+json" \
-H "Authorization: Bearer ${TOKEN}" \
-H "X-GitHub-Api-Version: 2026-03-10" \
https://api.github.com/orgs/ORG_NAME/properties/schema/PROPERTY_NAME \
-d '{"value_type":"string","required":false,"description":"SOME_DESCRIPTION","values_editable_by":"org_actors","require_explicit_values":false,"regex":"^\\d{5}$"}
```

creates/updates the regex values currently, without any issues.

### GitHub Installation Type

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

### Relevant log output

```shell

```

### Code of Conduct

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

Start at the github_organization_custom_properties resource and trace its schema update path to the /orgs/ORG_NAME/properties/schema/PROPERTY_NAME endpoint shown in the report. Check how Text properties are represented and where this resource’s existing tests live; done means regex validation can be configured for Text types without affecting other property types.

Written by the indexing model from the issue text.