/usr/share/mercurial/templates/spartan/ is in mercurial-common 4.0-1+deb9u1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/mercurial/templates/spartan/branches.tmpl
/usr/share/mercurial/templates/spartan/changelog.tmpl
/usr/share/mercurial/templates/spartan/changelogentry.tmpl
/usr/share/mercurial/templates/spartan/changeset.tmpl
/usr/share/mercurial/templates/spartan/error.tmpl
/usr/share/mercurial/templates/spartan/fileannotate.tmpl
/usr/share/mercurial/templates/spartan/filediff.tmpl
/usr/share/mercurial/templates/spartan/filelog.tmpl
/usr/share/mercurial/templates/spartan/filelogentry.tmpl
/usr/share/mercurial/templates/spartan/filerevision.tmpl
/usr/share/mercurial/templates/spartan/footer.tmpl
/usr/share/mercurial/templates/spartan/graph.tmpl
/usr/share/mercurial/templates/spartan/header.tmpl
/usr/share/mercurial/templates/spartan/index.tmpl
/usr/share/mercurial/templates/spartan/manifest.tmpl
/usr/share/mercurial/templates/spartan/map
/usr/share/mercurial/templates/spartan/notfound.tmpl
/usr/share/mercurial/templates/spartan/search.tmpl
/usr/share/mercurial/templates/spartan/shortlog.tmpl
/usr/share/mercurial/templates/spartan/shortlogentry.tmpl
/usr/share/mercurial/templates/spartan/tags.tmpl