Bump MimeKit from 3.3.0 to 4.7.1 in /MailBounceDetector

Bumps MimeKit from 3.3.0 to 4.7.1.

---
updated-dependencies:
- dependency-name: MimeKit
  dependency-type: direct:production
...

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

MailBounceDetector/MailBounceDetector.csproj

@@ -12,6 +12,6 @@
     <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="MimeKit" Version="3.3.0" />
+    <PackageReference Include="MimeKit" Version="4.7.1" />
   </ItemGroup>
 </Project>