chore(deps): update dependency mailkit to v4.6.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
MailKit (source)	4.5.0 -> 4.6.0

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Release Notes

jstedfast/MailKit (MailKit)

v4.6.0

Compare Source

• Swallow SMTP RSET exceptions. These obscure other Send/SendAsync exceptions. Fixes a regression
  introduced in 4.4.0. (issue #​1748)
• Fixed ImapUtils.FormatInternalDate() to properly handle negative timezone offsets with non-zero minutes.
  (issue #​1743)
• Bumped MimeKit dependency to 4.6.0.

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