Bump Verify.Xunit from 20.3.2 to 20.4.0 in /src

Bumps [Verify.Xunit](https://github.com/VerifyTests/Verify) from 20.3.2 to 20.4.0.
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](VerifyTests/Verify@20.3.2...20.4.0)

---
updated-dependencies:
- dependency-name: Verify.Xunit
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

src/Directory.build.props

@@ -52,7 +52,7 @@
     <PackageReference Include="Microsoft.Reactive.Testing" Version="6.0.0" />
     <PackageReference Include="PublicApiGenerator" Version="11.0.0" />
     <PackageReference Include="coverlet.msbuild" Version="6.0.0" PrivateAssets="All" />
-    <PackageReference Include="Verify.Xunit" Version="20.3.2" />
+    <PackageReference Include="Verify.Xunit" Version="20.4.0" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(IsTestProject)' != 'true'">