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

Root cause: Telemetry tests share host-level client across pytest-xdist workers,
causing test isolation issues with patches. Tests pass serially but fail with -n auto.

Solution: Add @pytest.mark.serial marker. CI needs to run these separately without -n auto.

Author: samikshya-db

pyproject.toml

@@ -62,7 +62,10 @@ exclude = ['ttypes\.py$', 'TCLIService\.py$']
 exclude = '/(\.eggs|\.git|\.hg|\.mypy_cache|\.nox|\.tox|\.venv|\.svn|_build|buck-out|build|dist|thrift_api)/'
 
 [tool.pytest.ini_options]
-markers = {"reviewed" = "Test case has been reviewed by Databricks"}
+markers = [
+    "reviewed: Test case has been reviewed by Databricks",
+    "serial: Tests that must run serially (not parallelized)"
+]
 minversion = "6.0"
 log_cli = "false"
 log_cli_level = "INFO"

tests/e2e/test_telemetry_e2e.py

@@ -43,8 +43,9 @@ def connection(self, extra_params=()):
             conn.close()
 
 
+@pytest.mark.serial
 class TestTelemetryE2E(TelemetryTestBase):
-    """E2E tests for telemetry scenarios"""
+    """E2E tests for telemetry scenarios - must run serially due to shared host-level telemetry client"""
 
     @pytest.fixture(autouse=True)
     def telemetry_setup_teardown(self):