Fix a whitespace issue

This wasn't flagged by Ruff, I should possibly just turn off the flake8 code.

Author: rwb27

src/labthings_fastapi/properties.py

@@ -363,12 +363,12 @@ def __init__(self, constraints: Mapping[str, Any] | None = None) -> None:
 
     constraints: Mapping[str, Any]
     """Validation constraints applied to this property.
-    
+
     This mapping contains keyword arguments that will be passed to
     `pydantic.Field` to add validation constraints to the property.
     See `pydantic.Field` for details. The module-level constant
     `CONSTRAINT_ARGS` lists the supported constraint arguments.
-    
+
     Note that these constraints will be enforced when values are
     received over HTTP, but they are not automatically enforced
     when setting the property directly on the `.Thing` instance