fix(recipe): add NCCL EP scan mode to DSv3 GB300 deterministic env

Megatron-Core's DETERMINISM_ENV_VAR_DEFAULTS on main now includes
NCCL_EP_HT_EM_AG_SCAN_MODE=1. Mirror it in the inline determinism
section so the recipe environment matches apply_determinism_overrides.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Zhiyu Li <zhiyul@nvidia.com>

Author: ZhiyuLi-Nvidia

src/megatron/bridge/perf_recipes/deepseek/gb300/deepseek_v3.py

@@ -215,6 +215,7 @@ def deepseek_v3_pretrain_256gpu_gb300_fp8mx_deterministic_config() -> ConfigCont
         # ---- Determinism (same values as apply_determinism_overrides) ----
         "CUBLAS_WORKSPACE_CONFIG": ":4096:8",
         "NCCL_ALGO": "Ring",
+        "NCCL_EP_HT_EM_AG_SCAN_MODE": "1",
         "NVTE_ALLOW_NONDETERMINISTIC_ALGO": "0",
         "MAMBA_DETERMINISTIC": "1",
         "CAUSAL_CONV1D_DETERMINISTIC": "1",