Declare `data` in jquery.endless-scroll

What does this MR do and why?

Declare data in jquery.endless-scroll

This ensures that data is defined in the vendored jquery.endless-scroll. This fixes a bug where endless scroll would not work in development when using Vite instead of Webpack.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After
before	after

How to set up and validate locally

• Enable Vite: https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/configuration.md#vite-settings
• Navigate to a commits page such as http://gdk.test:3000/jashkenas/Underscore/-/commits/master?ref_type=heads
• Scroll to the bottom of the page.
  • On this branch the next commits page should load.
  • On master, it should not, and an errors should be logged to the console.