fix: handle sharegpt dataset missing (#2035)

* fix: handle sharegpt dataset missing

* fix: explanation

* feat: add test

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

@@ -789,7 +789,12 @@ class AxolotlInputConfig(
             if not ds_cfg.get("type"):
                 continue
 
-            if ds_cfg["type"].startswith("sharegpt"):
+            ds_type = ds_cfg["type"]
+            # skip if it's a dict (for custom user instruction prompt)
+            if isinstance(ds_type, dict):
+                continue
+
+            if isinstance(ds_type, str) and ds_type.startswith("sharegpt"):
                 raise ValueError(
                     "`type: sharegpt.*` is deprecated. Please use `type: chat_template` instead."
                 )