Mark telemetry e2e tests as serial - must not run in parallel

The concurrent telemetry e2e test globally patches telemetry methods
to capture events. When run in parallel with other tests via pytest-xdist,
it captures telemetry events from other concurrent tests, causing
assertion failures (expected 60 events, got 88).

All telemetry e2e tests must run serially to avoid cross-test
interference with the shared host-level telemetry client.

Author: samikshya-db

tests/e2e/test_concurrent_telemetry.py

@@ -26,6 +26,7 @@ def run_in_threads(target, num_threads, pass_index=False):
         t.join()
 
 
+@pytest.mark.serial
 class TestE2ETelemetry(PySQLPytestTestCase):
     @pytest.fixture(autouse=True)
     def telemetry_setup_teardown(self):