Skip zmq/test_gnmi_zmq.py on all Arista platforms (sonic-net#17524)

What is the motivation for this PR?
The test is written for smartswitch as it enabled this mode unconditionally: https://github.com/sonic-net/sonic-mgmt/blob/master/tests/zmq/test_gnmi_zmq.py#L54-L58

As of now none of the Arista platforms operate in this mode.

How did you do it?
Add a conditional mark to skip this on Arista platforms.

How did you verify/test it?
Ran this test on Arista-7260CX3

zmq/test_gnmi_zmq.py::test_gnmi_zmq SKIPPED (Test is for smartswitch)

Author: vivekverma-arista

tests/common/plugins/conditional_mark/tests_mark_conditions.yaml

@@ -2691,3 +2691,12 @@ wan/lacp/test_wan_lag_min_link.py::test_lag_min_link:
     conditions:
       - "len(minigraph_portchannels) < 2"
       - "not any(len(v['members']) > 1 for _, v in minigraph_portchannels.items())"
+
+#######################################
+#####             zmq             #####
+#######################################
+zmq/test_gnmi_zmq.py:
+  skip:
+    reason: "Test is for smartswitch"
+    conditions:
+      - "'arista' in platform"