Fix “Alt text” button submitting form in moderation interface (#35147)

app/javascript/mastodon/components/alt_text_badge.tsx

@@ -33,6 +33,7 @@ export const AltTextBadge: React.FC<{
   return (
     <>
       <button
+        type='button'
         ref={anchorRef}
         className='media-gallery__alt__label'
         onClick={handleClick}