Bump Microsoft.NET.Test.Sdk from 18.6.0 to 18.7.0 (#393)

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.7.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Directory.Build.targets

@@ -22,7 +22,7 @@
 
   <!-- NuGet Dependencies -->
   <ItemGroup>
-    <PackageReference Update="Microsoft.NET.Test.Sdk"                       Version="18.6.0" />
+    <PackageReference Update="Microsoft.NET.Test.Sdk"                       Version="18.7.0" />
     <PackageReference Update="Microsoft.SourceLink.GitHub"                  Version="10.0.300" />
     <PackageReference Update="Microsoft.VisualStudioEng.MicroBuild.Core"    Version="1.0.0" />
     <PackageReference Update="nunit"                                        Version="3.13.2" />