Update MailKit and MimeKit packages to 4.9.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
MailKit (source)	4.8.0 -> 4.9.0
MimeKit (source)	4.8.0 -> 4.9.0

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Release Notes

jstedfast/MailKit (MailKit)

v4.9.0

Compare Source

• Added an IMAP work-around for mail.ru which sometimes sends integer tokens as decimals in its responses.
  (issue #​1838)
• Added a workaround for GMail IMAP BODY responses that include multipart expressions without any children
  (e.g. ("ALTERNATIVE")). (issue #​1841)
• Fixed default system proxy to handle null credentials and check if the targetUri is bypassed.
  (issue #​1852)
• Dropped support for net6.0 (Microsoft support ended Nov 12, 2024).
• Bumped System.Threading.Tasks.Extensions dependency to 4.6.0.
• Bumped MimeKit dependency to 4.9.0.

jstedfast/MimeKit (MimeKit)

v4.9.0

Compare Source

• Started adding some DynamicallyAccessedMembers attributes for AOT compatibility.
• Refactored some code for AOT Compatibility (MimeKitLite is now 100% AOT Compatible but MimeKit still has
  issues related to SQLite database loading for the S/MIME certificate database).
  (MailKit issue #​10844)
• Fixed TextPreviewer to use an encoding with an empty string fallback to prevent '?' characters from
  being appended to the generated preview string if the byte sequence was truncated.
• Improved performance of InternetAddressList.Parse()/TryParse().
• Improved InternetAddressList parser performance for malformed addresses that only contain
  display-name strings separated by commas.
  (issue #​1106)
• Exposed BouncyCastleCertificateExtensions.IsSelfSigned(), GetKeyUsageFlags() and IsDelta() as new public APIs.
• Exposed X509KeyUsageBits enum as public.
• Added support for domain-bound S/MIME certificates. (issue #​1113)
• Dropped support for net6.0 in the nuget packages (Microsoft support ended Nov 12, 2024).
• Removed explicit dependency on System.Runtime.CompilerServices.Unsafe.
• Bumped System.Security.Cryptography.Pkcs dependency to v8.0.1.
• Bumped BouncyCastle.Cryptography dependency to v2.5.0.
• Bumped System.Buffers dependency to v4.6.0.
• Bumped System.Memory dependency to v4.6.0.

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