Ensure postgresql_new is included in GitLab CE
Postgres 17 has been added in !9069 (merged) but is not available in GitLab CE.
The same happened when support for Postgres 16 has been introduced as was fixed shortly after via !7994 (merged)
Two additional findings which haven't been addressed in this PR:
- the docs have not been updated -> https://docs.gitlab.com/administration/package_information/postgresql_versions/
- the release blog post for 18.9 is not mentioning the addition of PG 17 (that was the case for previous updates)