databases/postgresql-jdbc: update to 42.3.6

The JDBC team has released version 42.3.6 to fix a regression introduced
in 42.3.2

This fixes "cursor <unnamed portal 1> does not exist" when using
ResultSet.setFetchSize from CallableStatement, fixed in 42.3.5
(see PG #2377)

Release notes: https://jdbc.postgresql.org/documentation/changelog.html#version_42.3.6