Bump MimeKit from 2.13.0 to 2.15.1

[dependabot]

Bumps MimeKit from 2.13.0 to 2.15.1.

Changelog

Sourced from MimeKit's changelog.

MimeKit 2.15.1 (2021-09-13)

• Improved MimeParser to be a little more efficient based on work being done for the upcoming v3.0 release.
• Fixed a bug in the MimeParser exposed by added unit tests regarding Content-Length handling.
• Improved address parser error messages.
• Fixed MailboxAddress.Address to be forgiving if there is trailing whitespace after the addr-spec token when setting MailboxAddress.Address. (issue #705)
• Fixed MimeMessage and MimeEntity.ToString() to not write a newline before the message/entity (regression introduced in 2.14.0).

MimeKit 2.15.0 (2021-08-18)

• Use DebugType=full for .NET Framework v4.x. (MailKit issue #1239)
• Fixed bug in MultipartSigned.VerifyAsync() that would dispose of the crypto context before the async task was complete, resulting in an OperationCanceledException.
• Default to using the Environment.SpecialFolder.UserProfile directory instead of Personal when GNUPGHOME isn't defined in the environment. The Personal directory maps to the MyDocuments directory, so this wasn't correct. The .gnupg directory should be in the user's HOME directory.
• Added ContentType.ToString(bool encode) and ContentDisposition.ToString(bool encode) convenience methods.
• Changed the public Header.Parse/TryParse APIs to canonicalize header values to end with a newline even if the input string does not. (issue #695)

MimeKit 2.14.0 (2021-07-28)

• Allow ..'s and trailing .'s in the local-part of an addr-spec by introducing a new RfcComplianceMode.Looser enum value that can be set on the ParserOptions.AddressParserComplianceMode property. (issue #682)
• Use Reflection to call Encoding.RegisterProvider() so that referencing the netstandard MimeKit assemblies from .NET 4.8 won't crash. (issue #683)
• Don't write the X-MimeKit warning header in ToString() anymore. This is a lost cause.
• Updated the OpenPgpContext to default to keys.openpgp.org since keys.gnupg.net does not resolve via DNS anymore.

Commits

• ad346be Bumped version to 2.15.1
• 6c3e3f3 Fixed a logic bug in MimeParser.StepHeaders() introduced in a previous simpli...
• c96710a Variable renaming in Multipart.WriteTo()
• 9c42eeb Fixed MimeMessage and MimeEntity.ToString() to not write a newline before the...
• 8a321a2 Added more MimeParser unit tests and removed unneeded code
• 11ac9e8 Added more MimeParser tests for message/rfc822 handling
• 8bcfbfb Simplified MimeParser.StepHeaders() logic for rewinding a byte if last char w...
• 8467b75 Improved MimeParser.StepMboxMarker() logic
• c3a53ee Added unit tests for MimeParser corner cases
• ac837bc Removed shortcut logic in MeasureingStream.Seek()
• Additional commits viewable in compare view

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[valadas]

@bdukes do we need to update the MailKit package manifest or is that automated by the build ?

[valadas]

Like run a build from this branch and commit the changed manifest maybe?

[bdukes]

The manifest is automatically updated, except for the version number in the release notes

[bdukes]

I went ahead and updated the manifest and also included the MailKit bump in this PR also, since they're packaged together anyway.

[valadas]

Excellent, thanks!