Bump Microsoft.NET.Test.Sdk from 17.12.0 to 18.7.0

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

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

Author: dependabot[bot]

SW.HttpExtensions.UnitTests/SW.HttpExtensions.UnitTests.csproj

@@ -8,7 +8,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.Http" Version="2.3.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="3.7.1" />
     <PackageReference Include="MSTest.TestFramework" Version="3.7.1" />
     <PackageReference Include="coverlet.collector" Version="6.0.4">