[AMD] Fix JSON mode streaming test flake on AMD CI (#20293)

test/registered/openai_server/features/test_json_mode.py

@@ -10,6 +10,7 @@ from sglang.test.test_utils import (
     DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
     DEFAULT_URL_FOR_TEST,
     CustomTestCase,
+    is_in_amd_ci,
     popen_launch_server,
 )
 
@@ -106,6 +107,9 @@ class ServerWithGrammarBackend(CustomTestCase):
             cls.backend,
         ]
 
+        if is_in_amd_ci():
+            other_args.append("--constrained-json-disable-any-whitespace")
+
         cls.process = popen_launch_server(
             cls.model,
             cls.base_url,