[Glitch] Fix spoiler toggle button being able to submit compose form

Port 1b8d1cd6e4 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/components/status_banner.tsx

@@ -49,6 +49,7 @@ export const StatusBanner: React.FC<{
 
       <button
         ref={buttonRef}
+        type='button'
         className='link-button'
         onClick={onClick}
         aria-describedby={descriptionId}