Fix: Deleting vertex group attribute can change original mesh

There was an error with the attribute API implementation for vertex
groups. If the vertex group layer referenced an original mesh, it wasn't
properly duplicated for writing.

source/blender/blenkernel/intern/geometry_component_mesh.cc

@@ -1049,6 +1049,11 @@ class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
     if (mesh->dvert == nullptr) {
       return true;
     }
+
+    /* Copy the data layer if it is shared with some other mesh. */
+    mesh->dvert = (MDeformVert *)CustomData_duplicate_referenced_layer(
+        &mesh->vdata, CD_MDEFORMVERT, mesh->totvert);
+
     for (MDeformVert &dvert : MutableSpan(mesh->dvert, mesh->totvert)) {
       MDeformWeight *weight = BKE_defvert_find_index(&dvert, index);
       BKE_defvert_remove_group(&dvert, weight);