[CI] Fix SWA decode radix cache NIXL import (#39600)

test/registered/disaggregation/test_disaggregation_decode_radix_cache_swa.py

@@ -9,7 +9,6 @@ import unittest
 
 from test_disaggregation_decode_radix_cache import (
     DisaggregationDecodeRadixCacheTestMixin,
-    _has_nixl,
 )
 
 from sglang.test.ci.ci_register import register_cuda_ci
@@ -23,6 +22,14 @@ register_cuda_ci(est_time=365, stage="extra-b", runner_config="8-gpu-h200")
 SWA_SERVER_ARGS = ["--page-size", "64", "--attention-backend", "triton"]
 
 
+def _has_nixl():
+    try:
+        import nixl._api  # noqa: F401
+    except ImportError:
+        return False
+    return True
+
+
 @unittest.skipUnless(
     is_in_ci() or _has_nixl(),
     "NIXL is required for decode radix cache disaggregation coverage.",