Adding tgen pytest mark to couple of pfc snappi-tests. (sonic-net#19027)

Description of PR
Summary:
Added tgen in addition to multidut-tgen

Approach
What is the motivation for this PR?
to add missing coverage on tgen

How did you do it?
Added tgen pytest mark

How did you verify/test it?
Ran on a single dut switch

co-authorized by: [email protected]

Author: kamalsahu0001

tests/snappi_tests/pfc/test_m2o_fluctuating_lossless.py

@@ -12,7 +12,7 @@
 from tests.common.snappi_tests.snappi_test_params import SnappiTestParams
 from tests.snappi_tests.cisco.helper import disable_voq_watchdog                  # noqa: F401
 logger = logging.getLogger(__name__)
-pytestmark = [pytest.mark.topology('multidut-tgen')]
+pytestmark = [pytest.mark.topology('multidut-tgen', 'tgen')]
 
 
 @pytest.fixture(autouse=True, scope='module')

tests/snappi_tests/pfc/test_m2o_oversubscribe_lossy.py

@@ -12,7 +12,7 @@
 from tests.common.snappi_tests.snappi_test_params import SnappiTestParams
 from tests.snappi_tests.cisco.helper import disable_voq_watchdog                  # noqa: F401
 logger = logging.getLogger(__name__)
-pytestmark = [pytest.mark.topology('multidut-tgen')]
+pytestmark = [pytest.mark.topology('multidut-tgen', 'tgen')]
 
 
 @pytest.fixture(autouse=True, scope='module')