Bump XAMLTest from 1.0.0-ci393 to 1.0.0-ci400 (#3105)

Bumps [XAMLTest](https://github.com/Keboo/XamlTest) from 1.0.0-ci393 to 1.0.0-ci400.
- [Release notes](https://github.com/Keboo/XamlTest/releases)
- [Commits](https://github.com/Keboo/XamlTest/commits)

---
updated-dependencies:
- dependency-name: XAMLTest
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

Directory.packages.props

@@ -22,7 +22,7 @@
     <PackageVersion Include="ShowMeTheXAML.AvalonEdit" Version="2.0.0" />
     <PackageVersion Include="ShowMeTheXAML.MSBuild" Version="2.0.0" />
     <PackageVersion Include="VirtualizingWrapPanel" Version="1.5.7" />
-    <PackageVersion Include="XAMLTest" Version="1.0.0-ci393" />
+    <PackageVersion Include="XAMLTest" Version="1.0.0-ci400" />
     <PackageVersion Include="xunit" Version="2.4.2" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="2.4.5" />
     <PackageVersion Include="Xunit.StaFact" Version="1.1.11" />