Bump the xunit group with 3 updates

Bumps the xunit group with 3 updates: [Verify.Xunit](https://github.com/VerifyTests/Verify), [System.Collections.Immutable](https://github.com/dotnet/runtime) and [System.Threading.Tasks.Extensions](https://github.com/dotnet/corefx).


Updates `Verify.Xunit` from 25.0.3 to 25.0.4
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](VerifyTests/Verify@25.0.3...25.0.4)

Updates `System.Collections.Immutable` from 1.5.0 to 8.0.0
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](https://github.com/dotnet/runtime/commits/v8.0.0)

Updates `System.Threading.Tasks.Extensions` from 4.5.0 to 4.5.4
- [Release notes](https://github.com/dotnet/corefx/releases)
- [Commits](https://github.com/dotnet/corefx/commits)

---
updated-dependencies:
- dependency-name: Verify.Xunit
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: xunit
- dependency-name: System.Collections.Immutable
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: xunit
- dependency-name: System.Threading.Tasks.Extensions
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: xunit
...

Signed-off-by: dependabot[bot] <support@github.com>

Tests/Approval.Tests/Approval.Tests.csproj

@@ -13,7 +13,7 @@
     </PackageReference>
     <PackageReference Include="PublicApiGenerator" Version="11.1.0" />
     <PackageReference Include="Verify.DiffPlex" Version="3.0.0" />
-    <PackageReference Include="Verify.Xunit" Version="25.0.3" />
+    <PackageReference Include="Verify.Xunit" Version="25.0.4" />
   </ItemGroup>
 
 </Project>