Graph Lines are not rendered when using Experimental GraphView or GridBackground

Reproduction steps:
1. Open the attached project "ReproProj"
2. Observe the Tree Editor (Window > UI Toolkit > Tree Editor)

Expected result: The Tree Editor window contains grid lines
Actual result: The Tree Editor window contains no grid lines

Reproducible with: 6000.0.53f1, 6000.1.11f1, 6000.2.0b9, 6000.3.0a1
Could not test with: 2022.3.62f1 (Assets\Editor\TreeGraphView.cs(7,6): error CS0246: The type or namespace name 'UxmlElementAttribute' could not be found)

Testing environment: Windows 10 Enterprise 21H2
Not reproducible on: No other environment tested

Notes:

• Reproducible with GraphView and GridBackground
• The RectangleSelector or other Grid Background features are working
• The Added Manipulators are working as intended