update to postgres 15rc2

[ImreSamu]

"PostgreSQL 15 RC 2 Released!" https://www.postgresql.org/about/news/postgresql-15-rc-2-released-2521/

STEPS:

• git mv 15rc1-3.3 15rc2-3.3
• git mv 15rc1-master 15rc2-master
• make update
• modify
  • README.md
  • `.github/workflows/main.yml

[ImreSamu]

Ready to review ( merge )