[Security] Bump phpmailer/phpmailer from 6.3.0 to 6.4.1 (#1456)

Bumps [phpmailer/phpmailer](https://github.com/PHPMailer/PHPMailer) from 6.3.0 to 6.4.1. **This update includes a security fix.**
- [Release notes](https://github.com/PHPMailer/PHPMailer/releases)
- [Changelog](https://github.com/PHPMailer/PHPMailer/blob/master/changelog.md)
- [Commits](https://github.com/PHPMailer/PHPMailer/compare/v6.3.0...v6.4.1

)

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