databases/postgresql19-*: Update to 19.0-beta4

This release contains PostgreSQL 19 feature previews ahead of general
availability, though some details of the release can change during the
beta period.

The next planned release of PostgreSQL 19 is the release candidate,
which should occur in early October. Based on testing and evaluation,
this means that the PostgreSQL 19 GA may also occur in October. More
details will be provided as we move closer to these releases.

This beta release reverted several features that were originally planned
for PostgreSQL 19. The PostgreSQL community strongly believes that,
first and foremost, PostgreSQL must be reliable. Additionally, the
community strives for a predictable release schedule. Because of this,
the community chose to remove some features from the PostgreSQL 19
release so they can be potentially be included in a later major release
after more time working through the community development and review
process.

Release notes: https://www.postgresql.org/about/news/postgresql-19-beta-4-released-3386/