PHP 8.1 is now the minimum supported runtime (#748)

### Changes

<!--
  Please outline the changes made in this pull request.
-->

### References

<!--
  Link to any associated issues, pull requests, or other resources.
-->

### Testing

<!--
  Tests must be added for new functionality.
  Existing tests should complete without errors.
  100% test coverage is required.
-->

### 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).

composer.json

@@ -28,7 +28,7 @@
   ],
   "homepage": "https://github.com/auth0/auth0-PHP",
   "require": {
-    "php": "^8.0",
+    "php": "^8.1",
     "ext-json": "*",
     "ext-mbstring": "*",
     "ext-openssl": "*",