Update imas_validator/assets/rulesets/generic/equilibrium.py

Following Copilot suggestion

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: MasanariHosokawa

imas_validator/assets/rulesets/generic/equilibrium.py

@@ -12,7 +12,9 @@ def validate_cocos(ids):
     """
 
     ver = str(ids.ids_properties.version_put.data_dictionary.value)[0]
-    ref = dd_cocos[ver]
+    ref = dd_cocos.get(ver)
+    if ref is None:
+        raise ValueError(f"Unsupported DD version_put: {ver}")
 
     # time_slice[:]
     for itime, time_slice in enumerate(ids.time_slice):