Fix alias env var error

Author: joaodaher

flamingo/models/base.py

@@ -24,5 +24,8 @@ def as_str(self) -> str:
     def as_kv(self):
         return f'{self.key}={self.value}'
 
+    def __str__(self):
+        return self.as_kv
+
 
 KeyValue = Dict[str, Any]

flamingo/services/alias_engine.py

@@ -32,7 +32,7 @@ def replace(self, virtual_value):
         try:
             replace_with = self.replacements[alias_to]
         except KeyError as e:
-            raise ValidationError(f"Could not find the referenced env var for {virtual_value.as_kv}") from e
+            raise ValidationError(f"Could not find the referenced value for {alias_to}") from e
 
         return re.sub(ALIAS_REGEX, replace_with, virtual_value)