Ignore test_snmp_phy_entity for 201911 images (#2625)

Skip test_snmp_phy_entity testcase on 201911 images. This testcase is primarily targeted to be executed on 202012 images.
Added a module scoped skip fixture. Executed the test on a 201911 image, and it was successfully skipped.

Author: vaibhavhd

tests/snmp/test_snmp_phy_entity.py

@@ -3,6 +3,7 @@
 import time
 
 from tests.common.utilities import wait_until
+from tests.common.helpers.assertions import pytest_require
 from tests.platform_tests.thermal_control_test_helper import mocker_factory
 
 pytestmark = [
@@ -99,6 +100,13 @@
 XCVR_DOM_KEY_TEMPLATE = 'TRANSCEIVER_DOM_SENSOR|{}'
 
 
+@pytest.fixture(autouse=True, scope="module")
+def check_image_version(duthost):
+    """Skip the test for unsupported images."""
+    pytest_require("201911" not in duthost.os_version, "Test not supported for 201911 images. Skipping the test")
+    yield
+
+
 @pytest.fixture(scope="module")
 def snmp_physical_entity_info(duthost, localhost, creds):
     """