Note: fix will need backport to 9.x.x

Repro steps:
1. Create a Universal Unlit shader
2. Create an Add node
3. Right click the add node and click "Group Selection"
4. Click and drag the "Position" node and drag it into the group

Expected result: no error
Actual result: error is thrown, and stack node can be dropped somewhere outside of its intended location (doesn't seem to be any major side effects).