xml2_load.rs: Explicitly drop a Box::from_raw to free it
xml2_load.rs: Explicitly drop a Box::from_raw to free it

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Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/723>

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg