Bump Microsoft.NET.Test.Sdk, xunit and xunit.runner.visualstudio

Bumps Microsoft.NET.Test.Sdk from 17.12.0 to 18.5.1
Bumps xunit from 2.9.2 to 2.9.3
Bumps xunit.runner.visualstudio from 2.8.2 to 3.1.5

---
updated-dependencies:
- dependency-name: Microsoft.NET.Test.Sdk
  dependency-version: 18.5.1
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: test-tooling
- dependency-name: xunit
  dependency-version: 2.9.3
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: test-tooling
- dependency-name: xunit.runner.visualstudio
  dependency-version: 3.1.5
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: test-tooling
...

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

Author: dependabot[bot]

Directory.Packages.props

@@ -27,10 +27,10 @@
     <PackageVersion Include="Velopack" Version="0.0.1298" />
 
     <!-- Tests -->
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.5.1" />
     <PackageVersion Include="NSubstitute" Version="5.3.0" />
-    <PackageVersion Include="xunit" Version="2.9.2" />
-    <PackageVersion Include="xunit.runner.visualstudio" Version="2.8.2" />
+    <PackageVersion Include="xunit" Version="2.9.3" />
+    <PackageVersion Include="xunit.runner.visualstudio" Version="3.1.5" />
   </ItemGroup>
 
 </Project>