/usr/share/glib-2.0/schemas/ is in gthumb-data 3:3.3.1.is.3.2.7-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/glib-2.0/schemas/org.gnome.gthumb.change-date.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.comments.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.contact-sheet.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.convert-format.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.crop.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.enums.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.facebook.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.file-manager.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.flickr.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.gstreamer-tools.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.image-print.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.image-viewer.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.importer.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.photo-importer.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.picasaweb.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.pixbuf-savers.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.rename-series.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.resize-images.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.resize.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.rotate.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.slideshow.gschema.xml
/usr/share/glib-2.0/schemas/org.gnome.gthumb.webalbums.gschema.xml