Deprecation warning in src/JsonSchema/Constraints/Drafts/Draft07/FormatConstraint.php on line 281

The output of phpunit shows the following deprecation
```
PHP Deprecated:  idn_to_ascii(): INTL_IDNA_VARIANT_2003 is deprecated in /home/runner/work/json-schema/json-schema/src/JsonSchema/Constraints/Drafts/Draft07/FormatConstraint.php on line 281
```

This should be address as per PHP recommendations whilst the test still remain green.