Bump the xunit group with 2 updates

Bumps the xunit group with 2 updates: [Verify.Xunit](https://github.com/VerifyTests/Verify) and [System.Collections.Immutable](https://github.com/dotnet/runtime).


Updates `Verify.Xunit` from 26.3.1 to 26.4.2
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](VerifyTests/Verify@26.3.1...26.4.2)

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)

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

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

Tests/Approval.Tests/Approval.Tests.csproj

@@ -13,7 +13,7 @@
     </PackageReference>
     <PackageReference Include="PublicApiGenerator" Version="11.1.0" />
     <PackageReference Include="Verify.DiffPlex" Version="3.1.0" />
-    <PackageReference Include="Verify.Xunit" Version="26.3.1" />
+    <PackageReference Include="Verify.Xunit" Version="26.4.2" />
   </ItemGroup>
 
 </Project>