Bump Portable.BouncyCastle from 1.8.6 to 1.8.6.7

Bumps [Portable.BouncyCastle](https://github.com/novotnyllc/bc-csharp) from 1.8.6 to 1.8.6.7.
- [Release notes](https://github.com/novotnyllc/bc-csharp/releases)
- [Commits](https://github.com/novotnyllc/bc-csharp/commits)

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

Rnwood.Smtp4dev/Rnwood.Smtp4dev.csproj

@@ -28,7 +28,7 @@
 		<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="3.1.3" />
 		<PackageReference Include="MimeKit" Version="2.5.2" />
 		<PackageReference Include="Rnwood.SmtpServer" Version="3.1.0-ci0534" />
-		<PackageReference Include="Portable.BouncyCastle" Version="1.8.6" />
+		<PackageReference Include="Portable.BouncyCastle" Version="1.8.6.7" />
 		<PackageReference Include="System.Data.SQLite" Version="1.0.112" />
 		<PackageReference Include="System.Linq.Dynamic.Core" Version="1.0.23" />
 		<PackageReference Include="VueCliMiddleware" Version="3.1.1" />