Fix openapi viewer

What does this MR do and why?

Fixes a bug that causes the OpenAPI viewer not to load.

(no related issue, it's a bug I noticed while browsing the repo, likely introduced by 27b24d80)

Screenshots or screen recordings

Before	After
Source viewer was loaded	OpenAPI viewer is loaded

How to set up and validate locally

1. Open an OpenAPI file via the repository files browser (swagger.json)
2. The OpenAPI viewer should load as expected

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.