Fix GH-16151: Assertion failure in ext/dom/parentnode/tree.c

Unfortunately, old DOM allows attributes to be used as parent nodes.
Only text nodes and entities are allowed as children for

Fix GH-16151: Assertion failure in ext/dom/parentnode/tree.c

Unfortunately, old DOM allows attributes to be used as parent nodes.
Only text nodes and entities are allowed as children for these types of
nodes, because that's the constraint DOM and libxml give us.

Closes GH-16156.

show more ...