/usr/share/postgresql/9.6/extension/ is in postgresql-9.6-pgrouting-scripts 2.3.2+ds-2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/postgresql/9.6/extension/pgrouting--2.0.0--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting--2.0.1--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting--2.1.0--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting--2.2.0--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting--2.2.1--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting--2.2.2--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting--2.2.3--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting--2.2.4--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting--2.3.0--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting--2.3.1--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting--2.3.2.sql
/usr/share/postgresql/9.6/extension/pgrouting.control