Pass `$resource_type` to 'get_ancestors' filter.

The `$resource_type` argument was added to the `get_ancestors()` function in
[30141]. In that changeset, the documentation for the filter was updated to
indicate that it would receive `$resource_type` as a param, but the filter
itself was not updated accordingly.

Props tmatsuur, DrewAPicture.
Fixes #30843.
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git-svn-id: http://core.svn.wordpress.org/trunk@30975 1a063a9b-81f0-0310-95a4-ce76da25c4cd