Fix instance overrides page

What does this MR do and why?

This fixes a typebug with the instance integrations overrides page introduced in !71998 (merged).

How to set up and validate locally

1. Enable an integration for a project
   1. From a project page, go: Settings > Integrations
   2. Choose an integration. Tip: External Wiki is a simple integration.
   3. Populate its form
   4. Click "Save"
2. Visit instance admin integrations page
   1. from /admin, go: Settings > Integrations choose the same integration as above.
3. Click "Projects using custom settings"
   1. You should see the project in the list.

All pages should load without errors.

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.

Related to #289975 (closed)