sneaky fix, don't tell Darren

Author: willmcgugan

src/textual/filter.py

@@ -184,6 +184,7 @@ def __init__(self, dim_factor: float = 0.5) -> None:
             dim_factor: The factor to dim by; 0 is 100% background (i.e. invisible), 1.0 is no change.
         """
         self.dim_factor = dim_factor
+        super().__init__()
 
     def apply(self, segments: list[Segment], background: Color) -> list[Segment]:
         """Transform a list of segments.