[Bugfix] fix nightly multi-node EPLB tests' "DYNAMIC_EPLB=true" environment not working (#4223)

### What this PR does / why we need it?
fix nightly multi-node EPLB tests by adjusting
vllm_ascend\eplb\core\eplb_utils.py dynamic_eplb gate checking
### Does this PR introduce _any_ user-facing change?
no

- vLLM version: v0.11.0
- vLLM main:
2918c1b49c

---------

Signed-off-by: 白永斌 <baiyongbin3@h-partners.com>
Signed-off-by: 欧派果奶我还要 <47294568+845473182@users.noreply.github.com>
Co-authored-by: 白永斌 <baiyongbin3@h-partners.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

vllm_ascend/eplb/core/eplb_utils.py

@@ -22,6 +22,8 @@ import sys
 import torch
 from vllm.logger import logger
 
+import vllm_ascend.envs as envs_ascend
+
 
 def determine_default_expert_map(global_expert_num, world_size, rank_id,
                                  global_redundant_expert_num):
@@ -140,9 +142,10 @@ class EPLBParamUtils:
             return
         if not isinstance(dynamic_eplb, bool):
             raise TypeError("The dynamic_eplb is not bool.")
-        if dynamic_eplb and os.getenv("DYNAMIC_EPLB", "false") != "true":
+
+        if dynamic_eplb and envs_ascend.DYNAMIC_EPLB not in ("true", "1"):
             raise ValueError(
-                'Can not enable dynamic_eplb when not export DYNAMIC_EPLB="true".'
+                'Can not enable dynamic_eplb when DYNAMIC_EPLB is not set to "true" or "1".'
             )
 
     @staticmethod