Bump Microsoft.NET.Test.Sdk and xunit.runner.visualstudio (#55)

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: all-dependencies
- dependency-name: xunit.runner.visualstudio
  dependency-version: 3.1.5
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: all-dependencies
...

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

Author: dependabot[bot]

tests/Shortcodes.Tests/Shortcodes.Tests.csproj

@@ -9,9 +9,9 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.0" />
     <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">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>