Fix AttributeError in insert_node_before

[Pricstas]

This PR fixes a bug in insert_node_before where child.parent.insert(position, new_sibling) was incorrectly used.
Since docutils.nodes.Element does not have an insert method, the correct approach is to insert the new sibling into the children list instead.

Changes

• Replaced child.parent.insert(position, new_sibling) with child.parent.children.insert(position, new_sibling), ensuring proper insertion of nodes.

[github-actions]

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