[XPU] Enable qwen3.5 on XPU (#21668)

Co-authored-by: Ma Mingfei <mingfei.ma@intel.com>

python/sglang/test/ci/ci_register.py

@@ -30,6 +30,7 @@ class HWBackend(Enum):
     CUDA = auto()
     AMD = auto()
     NPU = auto()
+    XPU = auto()
 
 
 @dataclass
@@ -104,11 +105,22 @@ def register_npu_ci(
     return None
 
 
+def register_xpu_ci(
+    est_time: float,
+    suite: str,
+    nightly: bool = False,
+    disabled: Optional[str] = None,
+):
+    """Marker for XPU CI registration (parsed via AST; runtime no-op)."""
+    return None
+
+
 REGISTER_MAPPING = {
     "register_cpu_ci": HWBackend.CPU,
     "register_cuda_ci": HWBackend.CUDA,
     "register_amd_ci": HWBackend.AMD,
     "register_npu_ci": HWBackend.NPU,
+    "register_xpu_ci": HWBackend.XPU,
 }