"InvalidOperationException: Collection was modified" error thrown.

"InvalidOperationException: Collection was modified; enumeration operation may not execute" error thrown on undo operation after adding properties under category.

Steps to Repro:
1. Create a new URP Project
2. Create > shader Graph > Blank shader Graph > Open shader editor
3. Shader Graph window > blackboard window > add a category
4.Under category add float > add Vector 2 > Vector 3
5. Edit > undo Add shader input
6.Observe the "InvalidOperationException: Collection was modified"
error in the console

Expected Result: No errors thrown in the Console

Actual Result: "InvalidOperationException: Collection was modified"
error in the console

Reproducible in:2022.1.0a1, 2021.2.b3, 2021.2.0b1

Environment: Windows 10 and macOS 11.3

Note: Backboard organization category functionality is introduced for 2021.2.0b1