[BUG] PostgresPersistence does not correcly load data from database.

Module this issue is about

ptbcontrib/postgres_persistence/postgrespersistence.py

Steps to reproduce

1. Use specified module as persistence class.

2. Build your application loading the persistence.

3. Add some random data inside bot_data, as it is the only one usable before getting updates.

4. Generate an update so the persistence is updated in the database.

5. Restart the bot script.

Expected behaviour

Added data (step 3) should be correctly loaded from database, so *_data dictionaries should contain the same information they had before restarting bot script.

Actual behaviour

Even if database is actually updated, *_dict are empty, so persistence is not restored correctly.

Configuration

Operating System:
Distributor ID: Linuxmint
Release: 21.3

Version of Python, python-telegram-bot & dependencies:
Python 3.12
PTB 21.2

Please Note

This is the first time I'm trying to contribute, so sorry if something is not clear enough.

Start in ptbcontrib/postgres_persistence/postgrespersistence.py and reproduce the reported sequence: add data to bot_data, generate an update, then restart the bot. Trace the database loading path and verify that the *_data dictionaries contain the same values after restart; done means persistence data is restored instead of remaining empty.