docs: Update README.md (#750)

### Changes

This PR updates the README to identify PHP 8.1 as the new minimum
supported version, and adds the new PHP 8.3 release to the support
schedule.

### References

N/A

### Testing

N/A

### Contributor Checklist

- [x] I agree to adhere to the [Auth0 General Contribution
Guidelines](https://github.com/auth0/open-source-template/blob/master/GENERAL-CONTRIBUTING.md).
- [x] I agree to uphold the [Auth0 Code of
Conduct](https://github.com/auth0/open-source-template/blob/master/CODE-OF-CONDUCT.md).

Signed-off-by: Evan Sims <[email protected]>

Author: evansims

README.md

@@ -23,7 +23,7 @@ We also have tailored SDKs for [Laravel](https://github.com/auth0/laravel-auth0)
 
 ### Requirements
 
-- PHP 8.0+
+- PHP 8.1+
 - [Composer](https://getcomposer.org/)
 - PHP Extensions:
   - [mbstring](https://www.php.net/manual/en/book.mbstring.php)
@@ -112,9 +112,9 @@ Our support lifecycle mirrors the [PHP release support schedule](https://www.php
 
 | SDK Version | PHP Version | Support Ends |
 | ----------- | ----------- | ------------ |
-| 8           | 8.2         | Dec 2025     |
+| 8           | 8.3         | Nov 2026     |
+|             | 8.2         | Nov 2025     |
 |             | 8.1         | Nov 2024     |
-|             | 8.0         | Nov 2023     |
 
 We drop support for PHP versions when they reach end-of-life and cease receiving security fixes from the PHP Foundation. Please ensure your environment remains up to date so you can continue receiving updates for PHP and this SDK.