Update dependency MailKit 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

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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.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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