chore(deps): bump postgres from 16 to 18 in /docker

[dependabot]

Bumps postgres from 16 to 18.

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot show <dependency name> ignore conditions will show all of the ignore conditions of the specified dependency
• @dependabot ignore this major version will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this minor version will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)

[JArmandoAnaya]

Superseded by #483, merged as e8282a4, which carries this same tag bump plus the mount change it requires.

The tag alone does not start: from 18 the image keeps its cluster in a major-version subdirectory and its entrypoint exits 1 when it finds a mount on /var/lib/postgresql/data, empty volume or not. No required check covers it, because the service is behind a profile and nothing in CI starts it. main is on postgres:18 now, with the mount at /var/lib/postgresql.

[dependabot]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version. You can also ignore all major, minor, or patch releases for a dependency by adding an ignore condition with the desired update_types to your config file.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.