ci: add explicit step to copy xunit configuration to test output

Ensure xunit.runner.json is available to xUnit during test execution by
explicitly copying it after the build step. This guarantees the configuration
file is in place even if MSBuild's CopyToOutputDirectory doesn't work as
expected on the CI runner.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Copilot

.github/workflows/publish.yml

@@ -56,6 +56,9 @@ jobs:
       - name: Build in Release mode
         run: dotnet build graphify-dotnet.slnx -c Release --no-restore -p:Version=${{ steps.version.outputs.version }}
 
+      - name: Ensure xunit configuration is in place
+        run: cp src/tests/Graphify.Tests/xunit.runner.json src/tests/Graphify.Tests/bin/Release/net10.0/xunit.runner.json
+
       - name: Run all tests
         run: dotnet test graphify-dotnet.slnx -c Release --no-build --verbosity normal