Fix exception on null json / jsonb value in postgres

[vladimirkl]

Backport of https://github.com/zio/zio-quill/pull/3023

Checklist

• [x] Unit test all changes
• [x] Update README.md if applicable
• [x] Add [WIP] to the pull request title if it's work in progress
• [x] Squash commits that aren't meaningful changes

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