QueryBuilder: Fix type bugs for PostgreSQL backend

[rabbull]

In #6619 some bugs in QueryBuilder for PostgreSQL backend are found. Because the fixes are not directly related to the topic of the PR, a new PR is created to address these bugs.

Related tests will be delievered in #6619.

[GeigerJ2]

LGTM!

[codecov]

Codecov Report

Attention: Patch coverage is 11.11111% with 8 lines in your changes missing coverage. Please review.

Project coverage is 77.92%. Comparing base (37e5431) to head (854545e).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...rc/aiida/storage/psql_dos/orm/querybuilder/main.py	11.12%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6658      +/-   ##
==========================================
- Coverage   77.93%   77.92%   -0.01%     
==========================================
  Files         563      563              
  Lines       41662    41668       +6     
==========================================
  Hits        32464    32464              
- Misses       9198     9204       +6     

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