soften the EP check for ICI and DCN with GPUs and fix linter

Author: kocchop

src/MaxText/pyconfig.py

@@ -1397,8 +1397,12 @@ def using_sequence_parallelism(raw_keys) -> bool:
 
 
 def using_expert_parallelism(raw_keys) -> bool:
-  if int(raw_keys["ici_expert_parallelism"]) > 1 and int(raw_keys["dcn_expert_parallelism"]) > 1:
-    raise ValueError("Expert parallelism can only be enabled on ICI or DCN, not both.")
+  if (
+      int(raw_keys["ici_expert_parallelism"]) > 1
+      and int(raw_keys["dcn_expert_parallelism"]) > 1
+      and raw_keys["hardware"] == "tpu"
+  ):
+    raise ValueError("Expert parallelism can only be enabled on ICI or DCN on TPU, not both.")
   return int(raw_keys["ici_expert_parallelism"]) > 1 or int(raw_keys["dcn_expert_parallelism"]) > 1