Bump Microsoft.NET.Test.Sdk from 17.14.1 to 18.0.0

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

src/SourceBrowser/src/Directory.Packages.props

@@ -28,7 +28,7 @@
     <PackageVersion Include="Microsoft.CodeAnalysis.Analyzers" Version="4.14.0" />
 
     <!-- test dependencies -->
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.0" />
     <PackageVersion Include="MSTest.TestAdapter" Version="3.9.3" />
     <PackageVersion Include="MSTest.TestFramework" Version="3.9.3" />
     <PackageVersion Include="Selenium.WebDriver" Version="3.14.0" />