Temporary skip subnet decap test with issue since feature haven't bee…

…n added to yang model (#15947)

What is the motivation for this PR?
In sonic-net/sonic-utilities#3102, the feature comparing yang model with configDB was added to sonic-utilities submodule, but feature subnet decap haven't been added to yang model, so the PR test advancing sonic-utilities to buildimage would fail in subnet decap test.

How did you do it?
Created issue sonic-net/sonic-buildimage#21090 and temporary skip subnet decap test until issue resolved

How did you verify/test it?

tests/common/plugins/conditional_mark/tests_mark_conditions.yaml

@@ -321,11 +321,12 @@ decap/test_decap.py::test_decap[ttl=uniform, dscp=uniform, vxlan=set_unset]:
 
 decap/test_subnet_decap.py::test_vlan_subnet_decap:
   skip:
-    reason: "Supported only on T0 topology with KVM or broadcom td3 asic or mellanox asic, and available for 202405 release and later"
+    reason: "Supported only on T0 topology with KVM or broadcom td3 asic or mellanox asic, and available for 202405 release and later, need to skip on KVM testbed since subnet_decap feature haven't been added into yang model"
     conditions_logical_operator: or
     conditions:
       - "topo_type not in ['t0']"
       - "asic_type not in ['vs', 'mellanox'] and asic_gen not in ['td3']"
+      - "asic_type in ['vs'] and https://github.com/sonic-net/sonic-buildimage/issues/21090"
       - "release in ['202012', '202205', '202305', '202311']"
 
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