ci: use working test server on macOS

ci: use working test server on macOS

macos-14 can use PostgreSQL 18. I saw a failure trying to use 17; not
sure if it's still there but 18 works fine, so bump.

macos-13 better says on 17. Trying to "brew update" it will pull a
version that will try to compile docbook and takes forever to install. I
understand that avoid an upgrade we get a version that has a binary
package ("bottled", in this deranged naming convention).