Image diff is displayed incorrectly for webp files.

### The problem

When viewing the difference for `.webp` files, only the _2-up_ view is working correctly (not sure about the _difference_ view). In both _Swipe_ and _Onion Skin_ views, the new version is displayed as old + new. The images below explain the issue more clearly.

Here is the _2-up_ view

Here is the _Swipe_ view

Here is the _Onion Skin_ view

### Release version

3.3.14

### Operating system

Windows 11

### Steps to reproduce the behavior

1. Create a repo
2. Add a `.webp` image
3. commit your changes
4. Change the old `.webp` image
5. View the diff from _GitHub Desktop_

### Log files

_No response_

### Screenshots

_No response_

### Additional context

Here is the commit I took the screenshots from: https://github.com/espale-studios/website/commit/748296a6ea433f9a64705614437d6b52dfebf179

No source files, tests, or entry points are named. First reproduce the issue in GitHub Desktop using the listed steps and a changed .webp image, then compare the 2-up, Swipe, and Onion Skin views; done means each view displays the new image correctly without combining old and new content.

Written by the indexing model from the issue text.