clarified wp beta to also include rc version (#1936)

## Motivation for the change, related issues
During 6.7 release cycle, it wasn't clear if 
`"preferredVersions": {
            "wp":"beta"
}`
would also include release candidate versions. 
## Implementation details
Added a clarifying sentence [to this
page](https://wordpress.github.io/wordpress-playground/blueprints/data-format)
## Testing Instructions (or ideally a Blueprint)
 docs only change

---------

Co-authored-by: Bero <[email protected]>

packages/docs/site/docs/blueprints/03-data-format.md

@@ -55,7 +55,7 @@ The `landingPage` property tells Playground which URL to navigate to after the B
 The `preferredVersions` property declares your preferred PHP and WordPress versions. It can contain the following properties:
 
 -   `php` (string): Loads the specified PHP version. Accepts `7.0`, `7.1`, `7.2`, `7.3`, `7.4`, `8.0`, `8.1`, `8.2`, `8.3`, or `latest`. Minor versions like `7.4.1` are not supported.
--   `wp` (string): Loads the specified WordPress version. Accepts the last four major WordPress versions. As of June 1, 2024, that's `6.2`, `6.3`, `6.4`, or `6.5`. You can also use the generic values `latest`, `nightly`, or `beta`.
+-   `wp` (string): Loads the specified WordPress version. Accepts the last four major WordPress versions. As of June 1, 2024, that's `6.2`, `6.3`, `6.4`, or `6.5`. You can also use the generic values `latest`, `nightly`, or `beta`. To use a pre-release version of WordPress, `beta` will load the latest beta or release candidate versions of a release cycle (Beta or RC).
 
 ```js
 {