fix: support loading application/x-scratch3-sprite

Installing `scratch3` or `scratch3-bin` from the AUR may cause the
browser to report `*.sb3` files as `application/x-scratch3-sprite`. This
change makes it so that won't break loading those sprites.

packages/scratch-gui/src/lib/file-uploader.js

@@ -211,6 +211,7 @@ const soundUpload = function (fileData, fileType, storage, handleSound, handleEr
 const spriteUpload = function (fileData, fileType, spriteName, storage, handleSprite, handleError = () => {}) {
     switch (fileType) {
     case '':
+    case 'application/x-scratch3-sprite': // from AUR packages
     case 'application/zip': { // We think this is a .sprite2 or .sprite3 file
         handleSprite(new Uint8Array(fileData));
         return;