validation for fsdp and deepspeed (#1388) [skip ci]

* validation for fsdp and deepspeed

* make sure to return data

src/axolotl/utils/config/models/input/v0_4_1/__init__.py

@@ -989,3 +989,10 @@ class AxolotlConfigWCapabilities(AxolotlInputConfig):
             )
 
         return data
+
+    @model_validator(mode="before")
+    @classmethod
+    def check_fsdp_deepspeed(cls, data):
+        if data.get("deepspeed") and data.get("fsdp"):
+            raise ValueError("deepspeed and fsdp cannot be used together.")
+        return data