Pydantic 2.12 breaks JSON serialization

[mattwthompson]

Description

Pydantic broke JSON serialization of custom types (pydantic/pydantic#12348 (comment)) in release 2.12 (pydantic/pydantic#12348). Don't know if there plans to be a backwards-compatible fix.

Still investigating.

Reproduction

See logs such as here

The error commonly looks like

pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'pint.Quantity'>

[mattwthompson]

Not enough information for a fix - and changing the use of serialize_as_any is a sweeping change, so I'd like to avoid for now. To get things moving, I'm simply avoiding that version in tests (#1347)