fix(db-postgres): Fixes nested groups inside nested blocks

[rfdomingues98]

Description

fix #5880
It seems to be passing on all the existing tests that are related. I haven't tested this further to check for potential edge cases.

• I have read and understand the CONTRIBUTING.md document in this repository.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have added tests that prove my fix is effective or that my feature works
• Existing test suite passes locally with my changes

[DanRibbens]

I made the same fix to tabs and also removed the prefix.replace(). This should have been replaceAll, but I removed it instead since field joining characters are "_" anyways.