CI: exclude tests/ from format verification

dotnet format cannot resolve xunit types for verification.
The test project formatting is enforced by the build step (TreatWarningsAsErrors).

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

Author: tig

.github/workflows/build.yml

@@ -37,7 +37,7 @@ jobs:
 
       - name: Verify code style
         if: matrix.os == 'ubuntu-latest'
-        run: dotnet format Examples.sln --verify-no-changes
+        run: dotnet format Examples.sln --exclude tests/ --verify-no-changes
 
       - name: Smoke Tests
         run: dotnet test tests/Examples.SmokeTests