Update dependency phpmailer/phpmailer to v6.9.1

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
phpmailer/phpmailer	6.8.1 -> 6.9.1

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Release Notes

PHPMailer/PHPMailer (phpmailer/phpmailer)

v6.9.1

Compare Source

• Finalise SendOauth2 example

v6.9.0

Compare Source

• Add support for official release of PHP 8.3, add experimental support for PHP 8.4
• Add clearCustomHeader and replaceCustomHeader methods
• Add support for the XCLIENT SMTP extension with setSMTPXclientAttribute and getSMTPXclientAttributes methods
• Don't attempt opportunistic TLS when connecting to localhost
• Add package link and example showing how to use @​decomplexity's SendOauth2 wrapper
• Update example to show a better way of using an SMTP subclass
• Avoid some more deprecation warnings
• Update Danish and Polish translations
• Add Bengali and Assamese translations

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