pack.png does not support translucent pixels

The bug

If a pack.png texture file is included in a resource pack, and said file has translucent pixels, those pixels will be rendered as entirely opaque in the resource packs menu.

This is one of a small handful of UI element translucency bugs, with others being MC-165182, MC-174732, MC-192307, MC-200987, MC-251303 and MC-268171. It may be worth looking at all of these together.

How to reproduce

1. Download the attached resource pack
2. Navigate to the resource packs menu

Expected results

The pack icon would be translucent, since pack.png is itself translucent (check inside of the zip if you want to confirm this).

Actual results

It is not.