[bugfix] Fix prefill tbo disabled when --deepep-mode=auto (#14333)

Co-authored-by: Cheng Wan <wan4ch@gmail.com>

test/srt/ep/test_deepep_small.py

@@ -1,3 +1,4 @@
+import os
 import unittest
 from types import SimpleNamespace
 
@@ -224,6 +225,10 @@ class TestTBO(CustomTestCase):
                 "--max-running-requests",
                 "512",
             ],
+            env={
+                **os.environ,
+                "SGLANG_TBO_DEBUG": "1",
+            },
         )
 
     @classmethod
@@ -351,6 +356,10 @@ class TestMTPWithTBO(CustomTestCase):
                 "--max-running-requests",
                 "128",
             ],
+            env={
+                **os.environ,
+                "SGLANG_TBO_DEBUG": "1",
+            },
         )
 
     @classmethod