Return `206` with `op: "StepNotFound"` when no step found to run

[jpwilliams]

Summary

If a step is intended to be run and was not found due to non-determinism or a changed function, still return a 206 with the "StepNotFound" opcode.

This complements inngest/inngest#1715 to ensure we recover from these situations gracefully.

Checklist

• [ ] ~Added a docs PR that references this PR~ N/A Bug fix
• [ ] Added unit/integration tests
• [ ] Added changesets if applicable

Related

• inngest/inngest#1715

[changeset-bot[bot]]

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Latest commit: 0a1303bed7bd6d1357cc29a0a67658f65444fb10

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