Unskip testQosSaiHeadroomPoolWatermark on t0-d18u8s4 (sonic-net#19287)

Summary:
Fixes # (issue)
Unskip testQosSaiHeadroomPoolWatermark on t0-d18u8s4 topology.

Author: Gfrom2016

tests/common/plugins/conditional_mark/tests_mark_conditions.yaml

@@ -1773,7 +1773,7 @@ qos/test_qos_sai.py::TestQosSai::testQosSaiHeadroomPoolWatermark:
          and asic_type in ['cisco-8000']
          and https://github.com/sonic-net/sonic-mgmt/issues/12292 and hwsku in ['Force10-S6100'] and topo_type in ['t1-64-lag']"
       - "topo_type in ['m0', 'mx']"
-      - "topo_name not in ['t0', 't0-64', 't0-116', 't0-118', 't0-35', 't0-56', 't0-standalone-32', 't0-standalone-64', 't0-standalone-128', 't0-standalone-256', 'dualtor-56', 'dualtor-120', 'dualtor', 'dualtor-aa', 't0-80', 't0-backend', 't1-lag', 't1-28-lag', 't1-48-lag', 't1-64-lag', 't1-56-lag', 't1-backend', 't2', 't2_2lc_36p-masic', 't2_2lc_min_ports-masic'] and asic_type not in ['mellanox']"
+      - "topo_name not in ['t0', 't0-64', 't0-116', 't0-118', 't0-35', 't0-56', 't0-standalone-32', 't0-standalone-64', 't0-standalone-128', 't0-standalone-256', 'dualtor-56', 'dualtor-120', 'dualtor', 'dualtor-aa', 't0-80', 't0-backend', 't1-lag', 't1-28-lag', 't1-48-lag', 't1-64-lag', 't1-56-lag', 't1-backend', 't2', 't2_2lc_36p-masic', 't2_2lc_min_ports-masic', 't0-d18u8s4'] and asic_type not in ['mellanox']"
   xfail:
     reason: "Headroom pool size not supported."
     conditions: