Remove parallel test execution in CI workflow

- Updated `.github/workflows/test-h3daemon.yml` to modify the testing command
- Changed `pytest -n 30` to `pytest` to disable parallel execution

Running tests without parallelism can help identify flaky tests and ensure
sequential data-dependent tests pass consistently without concurrency issues. 🛠️

.github/workflows/test-h3daemon.yml

@@ -25,4 +25,4 @@ jobs:
       - name: Run tests
         run: |
           pipx run poetry install
-          pipx run poetry run pytest -n 30
+          pipx run poetry run pytest