fix(dp-attn): consistent overlap disable decision across DP ranks (#20853)

test/registered/distributed/test_dp_attention.py

@@ -38,6 +38,10 @@ class TestDPAttentionDP2TP2(
     def setUpClass(cls):
         cls.model = DEFAULT_MLA_MODEL_NAME_FOR_TEST
         cls.base_url = DEFAULT_URL_FOR_TEST
+        cls._env_override = envs.SGLANG_DISABLE_CONSECUTIVE_PREFILL_OVERLAP.override(
+            True
+        )
+        cls._env_override.__enter__()
         cls.process = popen_launch_server(
             cls.model,
             cls.base_url,
@@ -58,6 +62,7 @@ class TestDPAttentionDP2TP2(
     @classmethod
     def tearDownClass(cls):
         kill_process_tree(cls.process.pid)
+        cls._env_override.__exit__(None, None, None)
 
     def test_mgsm_en(self):
         args = SimpleNamespace(