Bump MimeKit from 3.6.0 to 4.3.0

Bumps [MimeKit](https://github.com/jstedfast/MimeKit) from 3.6.0 to 4.3.0.
- [Changelog](https://github.com/jstedfast/MimeKit/blob/master/ReleaseNotes.md)
- [Commits](jstedfast/MimeKit@3.6.0...4.3.0)

---
updated-dependencies:
- dependency-name: MimeKit
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

context.tests/context.tests.csproj

@@ -74,9 +74,9 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
-    <PackageReference Include="MimeKit" Version="3.6.0" />
+    <PackageReference Include="MimeKit" Version="4.3.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
-    <PackageReference Include="MimeKit" Version="3.6.0" />
+    <PackageReference Include="MimeKit" Version="4.3.0" />
     <PackageReference Include="xunit" Version="2.5.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.0">
       <PrivateAssets>all</PrivateAssets>

context/context.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
     <Product>DirectProject.DotNet.Context</Product>
@@ -33,7 +33,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="MimeKit" Version="3.6.0" />
+    <PackageReference Include="MimeKit" Version="4.3.0" />
   </ItemGroup>
 
   <ItemGroup>