Fix CI test failure: Prevent parallel execution of telemetry tests

Add @pytest.mark.xdist_group to telemetry test classes to ensure they
run sequentially on the same worker when using pytest-xdist (-n auto).

Root cause: Tests marked @pytest.mark.serial were still being
parallelized in CI because pytest-xdist doesn't respect custom markers
by default. With host-level telemetry batching (PR #718), tests
running in parallel would share the same TelemetryClient and interfere
with each other's event counting, causing test_concurrent_queries_sends_telemetry
to see 88 events instead of the expected 60.

The xdist_group marker ensures all tests in the "serial_telemetry"
group run on the same worker sequentially, preventing state interference.

Signed-off-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: msrathore-db

tests/e2e/test_concurrent_telemetry.py

@@ -27,6 +27,7 @@ def run_in_threads(target, num_threads, pass_index=False):
 
 
 @pytest.mark.serial
+@pytest.mark.xdist_group(name="serial_telemetry")
 class TestE2ETelemetry(PySQLPytestTestCase):
     @pytest.fixture(autouse=True)
     def telemetry_setup_teardown(self):

tests/e2e/test_telemetry_e2e.py

@@ -44,6 +44,7 @@ def connection(self, extra_params=()):
 
 
 @pytest.mark.serial
+@pytest.mark.xdist_group(name="serial_telemetry")
 class TestTelemetryE2E(TelemetryTestBase):
     """E2E tests for telemetry scenarios - must run serially due to shared host-level telemetry client"""