How to reproduce:
1. Create a new URP Unity Project
2. In the Project window, right-click -> Shader Graph -> URP -> Lit Shader Graph
3. In the Shader Graph, right-click on the Blackboard
4. Observe the results

Expected results: No contextual menu opens because there is no contextual menu in Blackboard
Actual results: The Shader Graph contextual menu opens

Reproducible with: 2023.2.0a6, 6000.0.23f1
Not reproducible with: 2021.3.44f1, 2022.3.49f1, 2023.2.0a5

Reproducible on: macOS Sequoia 15.0 (M1)
Not reproducible on: No other environment tested