Bump MimeKit from 4.11.0 to 4.15.1

---
updated-dependencies:
- dependency-name: MimeKit
  dependency-version: 4.15.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

context/context.csproj

@@ -33,7 +33,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="MimeKit" Version="4.11.0" />
+    <PackageReference Include="MimeKit" Version="4.15.1" />
   </ItemGroup>
 
   <ItemGroup>