fix: use real, actual javascript in api generators

[pepopowitz]

Description

While investigating #3736, I discovered that the error handling in the API generator code doesn't actually run 😰.

This is not really a significant issue because the only way to find it is to improperly call the API generators, but it's probably better to actually tell people how they're misusing them.

For what it's worth, I'm pretty sure GitHub Copilot wrote these blocks for me, demonstrating again that computers should never be trusted.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.

• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

• My changes require a docs infrastructure review.