Bump Verify.Nunit from 26.5.0 to 26.6.0 in /src (#588)

Author: dependabot[bot]

src/Directory.Packages.props

@@ -12,6 +12,6 @@
     <PackageVersion Include="SixLabors.ImageSharp" Version="3.1.5" />
     <PackageVersion Include="Verify" Version="26.6.0" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.0" />
-    <PackageVersion Include="Verify.Nunit" Version="26.5.0" />
+    <PackageVersion Include="Verify.Nunit" Version="26.6.0" />
   </ItemGroup>
 </Project>