When releasing a mesh from a `GeometrySet` one has to take manual control over
owner-management. In some cases, the geometry set was not the owner of the mesh,
but was just referencing it. This is generally fine in a limited set of
circumstances and can avoid copies. However, when taking ownership of the mesh
in the geometry set, one has to be sure that the geometry set actually has
ownership.
This is similar to what is done in e.g. `modifier_modify_mesh_and_geometry_set`.
Pull Request: https://projects.blender.org/blender/blender/pulls/137150
bf5339df14