Module checks wrong content type in browser Accept header

I am not entirely sure this check if useful because we already use a <picture> HTML tag to let the browser get the AVIF image only if it supports this format.
And checking for image/avif to be explicitly in the Accept header could be a bit too strict, because browsers can send */* in this header.

Just noticed this is the same fix as 🐛 ImageStyleDownloadController incorrectly checking for image/webp instead of image/avif Fixed .