Bump Xunit from 2.9.0 to 2.9.1 in /src (#534)

Author: dependabot[bot]

src/Directory.Packages.props

@@ -26,7 +26,7 @@
     <PackageVersion Include="Verify.ImageMagick" Version="3.5.0" />
     <PackageVersion Include="Verify.WinForms" Version="4.0.0" />
     <PackageVersion Include="Verify.Xunit" Version="26.6.0" />
-    <PackageVersion Include="Xunit" Version="2.9.0" />
+    <PackageVersion Include="Xunit" Version="2.9.1" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="3.0.0-pre.35" />
     <PackageVersion Include="XunitContext" Version="3.3.2" />
   </ItemGroup>