Fix QueryError.retriable serialization

[ethanyzhang]

Description

Fixed a mistake in QueryError.retriable serialization when sending client response. The field name was previously "boolean" instead of "retriable".

Motivation and Context

Impact

Applications that make use of this field may need to be updated.

Test Plan

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Release Notes

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[tdcmeehan]

Let's close this in favor of #19741 (which also has a unit test).