`eb.case`'s `then`, `thenRef`, `else` and `elseRef` might be too permissive.

[igalklebanov]

Hey 👋

Currently, then, thenRef*, else and elseRef* are too permissive at compile-time.

Engines like PostgreSQL will fail queries based on case return data type group mismatches.

Fail if there is not an implicit conversion from a given input type to the candidate type
https://www.postgresql.org/docs/current/typeconv-union-case.html

While engines like MySQL are accepting all combos.

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* pending release in 0.29.