💥 [DevOps] Refactor Backend Tests

Created by: ulfgebhardt

💥 DevOps ticket

Refactor flaky backend tests

• Only two database reset per test file (start & end)
• Find a way to reset the database after a successful test run (?)

Quick fix: Clean Database before and after every test to reduce flakiness.

• Done by PR #4565

For (most) tests remain to fix search for comment: // TODO: avoid database clean after each test in the future if possible for performance and flakyness reasons by filling the database step by step, see issue https://github.com/Ocelot-Social-Community/Ocelot-Social/issues/4543 To be sure to find all remainders do an own additional search, please!

There is a related PR #3469