ext/pgsql: Refactor tests (#12608)

This makes the tests independent of each other and allows them to be run in parallel.

Co-authored-by: Gina Peter Banyard <girgias@php.net>

Fix GH-10672 (pg_lo_open segfaults in the strict_types mode)

We need to use the proper ZPP qualifier for zend_string

Closes GH-10677