Bump Verify.Xunit from 28.7.1 to 28.8.1 in the xunit group

Bumps the xunit group with 1 update: [Verify.Xunit](https://github.com/VerifyTests/Verify).


Updates `Verify.Xunit` from 28.7.1 to 28.8.1
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](https://github.com/VerifyTests/Verify/commits)

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

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

Tests/Approval.Tests/Approval.Tests.csproj

@@ -14,7 +14,7 @@
     </PackageReference>
     <PackageReference Include="PublicApiGenerator" Version="11.3.0" />
     <PackageReference Include="Verify.DiffPlex" Version="3.1.2" />
-    <PackageReference Include="Verify.Xunit" Version="28.7.1" />
+    <PackageReference Include="Verify.Xunit" Version="28.8.1" />
   </ItemGroup>
 
   <ItemGroup>