Add missing finish_reason to OpenAI output types (#766)

## Summary
<!-- Succinctly describe your change, providing context, what you've
changed, and why. -->

Adds the missing `finish_reason: string` field to output types for
OpenAI calls.

## Checklist
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wrapping it in "~~"" and suffix it with "N/A My reason for skipping
this." -->
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- [ ] ~Added a [docs PR](https://github.com/inngest/website) that
references this PR~ N/A Bug fix
- [ ] ~Added unit/integration tests~ N/A
- [x] Added changesets if applicable

## Related
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<!-- e.g. - INN-123 -->
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- Helps inngest/agent-kit#17

.changeset/lemon-sloths-wave.md

@@ -0,0 +1,5 @@
+---
+"inngest": patch
+---
+
+Add missing `finish_reason` to OpenAI output types

packages/inngest/src/components/ai/adapters/openai.ts

@@ -355,6 +355,16 @@ export interface OpenAiAiAdapter extends AiAdapter {
        * greater than 1.
        */
       choices: {
+        /**
+         * The reason the model stopped generating tokens. This will be `stop`
+         * if the model hit a natural stop point or a provided stop sequence,
+         * `length` if the maximum number of tokens specified in the request was
+         * reached, `content_filter` if content was omitted due to a flag from
+         * our content filters, `tool_calls` if the model called a tool, or
+         * `function_call` (deprecated) if the model called a function.
+         */
+        finish_reason: string;
+
         /**
          * The index of the choice in the list of choices.
          */