Support single value in require_one_of_values

cvat/apps/engine/field_validation.py

@@ -26,10 +26,17 @@ def require_field(data: dict[str, Any], key: str) -> None:
 
 
 def require_one_of_values(data: dict[str, Any], key: str, values: Sequence[Any]) -> None:
+    assert values
+
     if data[key] not in values:
-        raise serializers.ValidationError(
-            '"{}" must be one of {}'.format(key, ", ".join(f"{k}" for k in values))
-        )
+        if len(values) == 1:
+            raise serializers.ValidationError(
+                'The "{}" field must be {}'.format(key, ", ".join(f"{k}" for k in values))
+            )
+        else:
+            raise serializers.ValidationError(
+                'The "{}" field must be one of {}'.format(key, ", ".join(f"{k}" for k in values))
+            )
 
 
 def validate_percent(value: float) -> float: