PNGs are converted to JPEG on upload

**Describe the bug**

When I upload a png file, either as a post image or an inline image it is converted to jpg.

**To Reproduce**

1. Create a new post or comment.
2. Upload a png (preferably with transparency to see immediately if it worked)
3. Save post or comment.

**Expected behavior**

Image is rendered as a png with transparency.

**Smartphone (please complete the following information):**

- Device: Fairphone 3
- OS: Android 13
- native App
- Version: 2.30.1

**Additional context**

I saw this already with 2.29.0, maybe a version or two earlier. If I recall correctly it did work before that.

Uploading PNGs via Lemmy's web interface works.