Bump the tests group with 2 updates

Bumps Microsoft.NET.Test.Sdk from 17.13.0 to 18.0.0
Bumps xunit.runner.visualstudio from 3.1.0 to 3.1.5

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: tests
- dependency-name: xunit.runner.visualstudio
  dependency-version: 3.1.5
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: tests
...

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

Author: dependabot[bot]

src/ThisAssembly.Tests/ThisAssembly.Tests.csproj

@@ -48,10 +48,10 @@
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="all" />
     <PackageReference Include="PolySharp" Version="1.15.0" PrivateAssets="All" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.0.1" Pack="false" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.0" />
     <PackageReference Include="Scriban" Version="6.2.1" />
     <PackageReference Include="xunit" Version="2.9.3" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.0" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5" />
   </ItemGroup>
 
   <ItemGroup>