Bump the test-dependencies group with 2 updates (#1119)

Bumps Microsoft.NET.Test.Sdk from 18.7.0 to 18.8.1
Bumps NSubstitute from 5.3.0 to 6.0.0

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.8.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: test-dependencies
- dependency-name: NSubstitute
  dependency-version: 6.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: test-dependencies
...

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Author: dependabot[bot]

Directory.Packages.props

@@ -12,11 +12,11 @@
     <PackageVersion Include="Microsoft.CodeAnalysis.BannedApiAnalyzers" Version="5.6.0" />
     <PackageVersion Include="Microsoft.CodeAnalysis.NetAnalyzers" Version="10.0.301" />
     <PackageVersion Include="Microsoft.CodeAnalysis.PublicApiAnalyzers" Version="3.3.4" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.8.1" />
     <PackageVersion Include="Microsoft.Playwright" Version="1.61.0" />
     <PackageVersion Include="MinVer" Version="7.0.0" />
     <PackageVersion Include="NeoSmart.AsyncLock" Version="3.2.1" />
-    <PackageVersion Include="NSubstitute" Version="5.3.0" />
+    <PackageVersion Include="NSubstitute" Version="6.0.0" />
     <PackageVersion Include="NuGet.Versioning" Version="7.6.0" />
     <PackageVersion Include="NUnit" Version="4.6.1" />
     <PackageVersion Include="NUnit.Analyzers" Version="4.14.0" />