System Information
Operating system: Windows-10-10.0.19042-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 472.12

Blender Version
Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: rBf1cca3055776
Caused by rB3b6ee8cee708: Refactor: Move vertex group names to object data

Short description of error
When separating a grease pencil stroke to its own grease pencil object it will lose all vertex groups.

Exact steps for others to reproduce the error
a) create a new grease pencil object with the default stroke
b) create some vertex groups (optionally assign some weights)
c) select the stroke in edit mode and press P > choose "selected strokes"
d) when you go and edit the new GP object all the vertex groups on the stroke will have been deleted

Expected behavior:
The stroke will keep its vertex groups once its separated to its own grease pencil object.