Fix qos/test_qos_sai.py for t0-d18u8s4 (#21211)

Summary:
Add t0-d18u8s4 to SUPPORTED_T0_TOPOS
Skip testing 10G ports for qos/test_qos_sai.py on Arista-7050CX3-32S-C28S4/Arista-7050CX3-32C-C28S4

Author: byu343

tests/qos/qos_sai_base.py

@@ -46,7 +46,7 @@ class QosBase:
     Common APIs
     """
     SUPPORTED_T0_TOPOS = [
-        "t0", "t0-56", "t0-56-po2vlan", "t0-64", "t0-116", "t0-118", "t0-35", "dualtor-56", "dualtor-64",
+        "t0", "t0-56", "t0-56-po2vlan", "t0-64", "t0-116", "t0-118", "t0-35", "t0-d18u8s4", "dualtor-56", "dualtor-64",
         "dualtor-120", "dualtor", "dualtor-64-breakout", "dualtor-aa", "dualtor-aa-56", "dualtor-aa-64-breakout",
         "t0-120", "t0-80", "t0-backend", "t0-56-o8v48", "t0-8-lag", "t0-standalone-32", "t0-standalone-64",
         "t0-standalone-128", "t0-standalone-256", "t0-28", "t0-isolated-d16u16s1", "t0-isolated-d16u16s2",
@@ -62,6 +62,7 @@ class QosBase:
                            "td3", "th3", "j2c+", "jr2", "th5"]
 
     BREAKOUT_SKUS = ['Arista-7050-QX-32S']
+    LOW_SPEED_PORT_SKUS = ['Arista-7050CX3-32S-C28S4', 'Arista-7050CX3-32C-C28S4']
 
     TARGET_QUEUE_WRED = 3
     TARGET_LOSSY_QUEUE_SCHED = 0
@@ -1032,11 +1033,12 @@ def dutConfig(
             vlan_info = config_facts[src_dut.hostname].get('VLAN', {})
             port_speeds = self.__buildPortSpeeds(config_facts[src_dut.hostname])
             low_speed_portIds = []
-            if src_dut.facts['hwsku'] in self.BREAKOUT_SKUS and 'backend' not in topo:
+            if src_dut.facts['hwsku'] in self.BREAKOUT_SKUS + self.LOW_SPEED_PORT_SKUS and 'backend' not in topo:
                 for speed, portlist in port_speeds.items():
                     if int(speed) < 40000:
                         for portname in portlist:
-                            low_speed_portIds.append(src_mgFacts["minigraph_ptf_indices"][portname])
+                            if portname in src_mgFacts["minigraph_ptf_indices"]:
+                                low_speed_portIds.append(src_mgFacts["minigraph_ptf_indices"][portname])
 
             testPortIds[src_dut_index][src_asic_index] = set(src_mgFacts["minigraph_ptf_indices"][port]
                                                              for port in src_mgFacts["minigraph_ports"].keys())