chore(deps): update dependency mailkit to v4.2.0

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
MailKit (source)	nuget	minor	4.1.0 -> 4.2.0

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Release Notes

jstedfast/MailKit (MailKit)

v4.2.0

Compare Source

• Fixed a bug where the HttpProxyClient and HttpsProxyClient could end up reading the mail server greeting,
  causing a connection failure for the ImapClient/Pop3Client/SmtpClient.
  (issue #​1603)
• Parse IMAP quota values as ulongs instead of uints for GMail compatibility.
  (issue #​1602)
• Added support for decoding SMTP DATA to the SmtpDataFilter.
  (issue #​1607)
• Added a Pop3Client.Size property. (issue #​1623)
• Refactored more ImapClient commands to split sync/async implementations in order to improve
  performance and reduce GC pressure. (issue #​1335)
• Added new IMailFolder.GetStream() methods that just take a uid/index and a BodyPart.
• Added IMailFolder.GetStream/Async() methods that just take a uid or index.
• Improved initial List<IMessageSummary> capacity estimation for Fetch (IList<UniqueId>, ...).
• Fixed ByteArrayBuilder.TrimNewLine() to check array bounds properly.
  (issue #​1634)

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