[Fix] Land the decode mamba checkpoint depth on the tree page under DCP (#35412)

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-authored-by: Ke Bao <ispobaoke@gmail.com>

test/registered/unit/spec/test_ngram_mamba_verify_update.py

@@ -198,8 +198,8 @@ class TestNgramMambaVerifyUpdate(CustomTestCase):
             "sglang.srt.speculative.spec_utils.mambaish_config",
             return_value={"some": "config"},
         ), patch(
-            "sglang.srt.speculative.spec_utils.get_exec",
-            return_value=MagicMock(mamba=MagicMock(mamba_track_interval=256)),
+            "sglang.srt.speculative.spec_utils.mamba_track_grid",
+            return_value=256,
         ):
             commit_mamba_states_after_verify(
                 target_worker,