(maint) Update dependency Verify.Xunit to 30.15.0

Author: renovate[bot]

src/Diagramming.Tests/Diagramming.Tests.csproj

@@ -18,7 +18,7 @@
         </PackageReference>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
         <PackageReference Include="Moq" Version="4.20.72" />
-        <PackageReference Include="Verify.Xunit" Version="30.3.0" />
+        <PackageReference Include="Verify.Xunit" Version="30.15.0" />
         <PackageReference Include="xunit" Version="2.9.2"/>
         <PackageReference Include="xunit.analyzers" Version="1.18.0" />
         <PackageReference Include="xunit.runner.visualstudio" Version="3.0.0">