Update dependency MailKit to 4.18.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
MailKit (source)	4.17.0 → 4.18.0

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Release Notes

jstedfast/MailKit (MailKit)

v4.18.0

Compare Source

• Fixed SaslMechanismNativeNtlm on systems that need a multi-stage auth.
  (issue #​2007)
• Added support for the IMAP PARTIAL extension (rfc9294) for paged SEARCH/SORT and FETCH commands.
  (issue #​1687)
• Significantly improved IMAP performance by reusing internal buffers for building commands and
  reading responses.
• Fixed a few cases where IMAP did not properly use case-insenstive string comparisons when parsing
  some command responses. (issue #​2013)
• Do not default the ImapClient connection to IMAP4rev2 unless it is the only supported protocol version.
  (issue #​2016)
• Bumped System.Formats.Asn1 dependency from 8.0.1 to 10.0.0.
• Bumped MimeKit dependency from 4.17.0 to 4.18.0.

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