fix: modmore\Gitify\Command\ExtractCommand::extractPackages() – Implicitly marking parameter $file as nullable is deprecated

[jenswittmann]

Prevents this error when running gitify extract on PHP 8.3:

Deprecated: modmore\Gitify\Command\ExtractCommand::extractPackages(): Implicitly marking parameter $file as nullable is deprecated, the explicit nullable type must be used instead in /.composer/vendor/modmore/gitify/src/Command/ExtractCommand.php on line 500

[Copilot]

Pull Request Overview

This PR fixes a PHP 8.3 deprecation warning by explicitly marking a nullable parameter type in the ExtractCommand class.

• Updates parameter type declaration to use explicit nullable syntax (string|null instead of implicit nullable with default null)

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