"InvalidOperationException: Sequence contains more than one matching element" error is thrown when creating a new Property while a category with name "Position" exists

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Install the Visual Effect Graph package (com.unity.visualeffectgraph)
3. Create a new Visual Effect Graph (Assets > Create > Visual Effects > Visual Effect Graph)
4. Open the newly created Visual Effect Graph
5. Create a new Category named "Position" by clicking the "+" button in the Blackboard
6. Create a new Bool property by clicking the "+" button in the Blackboard
7. Observe the Blackboard and the Console window

Actual results: "InvalidOperationException: Sequence contains more than one matching element" error is thrown and no property is created

Expected results: No errors are thrown and a property is created

Reproducible with versions: 6000.0.0f1, 6000.0.83f1, 6000.3.24f1, 6000.5.11f1, 6000.6.1f1, 6000.7.0a6

Tested on (OS): MacOS Silicon Tahoe 26.6.2, Ubuntu 24.04