When the "use_attribute" properties were added, boolean IDProperties
didn't exist. Then we didn't change it for a while because of forward
compatibility concerns. But currently we always convert boolean
properties to integer properties when saving anyway (since
2ea47e0def, so there is no issue with compatibility.
Using booleans makes working with the properties in the Python API
a bit friendlier.
Pull Request: https://projects.blender.org/blender/blender/pulls/119129
01941e2b50