fixed postgre type mismatch error in mixins.py

[Tosinibikunle]

resolves #740

[2ykwang]

Thanks for the PR! @Tosinibikunle

I’m currently a bit busy with work, so I’ll be able to do a full review this weekend.

In the meantime, could you please:

• Confirm whether the mismatch error occurs in get_for_objects (from the issue description, it seems to be triggered in the “IN query”)
• Check if the same issue also happens in get_for_object
• Add a test case that covers this scenario

[hramezani]

Also add a changelog entry

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.88%. Comparing base (9ef8cf2) to head (d630437).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #746      +/-   ##
==========================================
+ Coverage   95.81%   95.88%   +0.06%     
==========================================
  Files          34       34              
  Lines        1194     1190       -4     
==========================================
- Hits         1144     1141       -3     
+ Misses         50       49       -1     

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[hramezani]

@2ykwang could you review it again?