Bump Microsoft.NET.Test.Sdk from 16.6.1 to 16.7.0

Bumps [Microsoft.NET.Test.Sdk](https://github.com/microsoft/vstest) from 16.6.1 to 16.7.0.
- [Release notes](https://github.com/microsoft/vstest/releases)
- [Commits](microsoft/vstest@v16.6.1...v16.7.0)

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

Rnwood.Smtp4dev.Tests/Rnwood.Smtp4dev.Tests.csproj

@@ -12,7 +12,7 @@
   <ItemGroup>
     <PackageReference Include="MailKit" Version="2.8.0" />
     <PackageReference Include="MedallionShell" Version="1.6.1" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.6.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.7.0" />
     <PackageReference Include="Selenium.Support" Version="3.141.0" />
     <PackageReference Include="Selenium.WebDriver" Version="3.141.0" />
     <PackageReference Include="Selenium.WebDriver.ChromeDriver" Version="84.0.4147.3001" />