Bump MailKit from 2.5.2 to 2.6.0
Bump MailKit from 2.5.2 to 2.6.0

Bumps [MailKit](https://github.com/jstedfast/MailKit) from 2.5.2 to 2.6.0.
- [Release notes](https://github.com/jstedfast/MailKit/releases)
- [Changelog](https://github.com/jstedfast/MailKit/blob/master/ReleaseNotes.md)
- [Commits](https://github.com/jstedfast/MailKit/compare/2.5.2...2.6.0)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
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