test(snapshot): tighten todo_write item schema in master's new acp snapshots
The origin/master merge added the session-query-spill and
escalation-approved acp scenarios, whose pinned tool-schemas still
carried additionalProperties: true on the todo_write item schema. This
PR tightens that to false (model-visible via the request header), so
re-record it in the two new expected outputs. session-sandbox-root,
escalation-rejected, and fs-escalation-approved compare against the
escalation-approved pinned header and pass once it is fixed.
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