Fix PictureField type hints (#212)

Author: amureki

pictures/models.py

@@ -244,10 +244,10 @@ def __init__(
         self,
         verbose_name=None,
         name=None,
-        aspect_ratios: [str | Fraction | None] = None,
+        aspect_ratios: list[str | Fraction | None] = None,
         container_width: int = None,
-        file_types: [str] = None,
-        pixel_densities: [int] = None,
+        file_types: list[str] = None,
+        pixel_densities: list[int] = None,
         grid_columns: int = None,
         breakpoints: {str: int} = None,
         **kwargs,