Test was designed to verify an old workaround when we were still using
imghdr. This workaround has been removed and there is no reason for it
to continue its existence in this universe...

Signed-off-by: Stephan Lachnit <[email protected]>

…rate colors when saving specific image files (#142)

* Add `transform_colorspace_to_srgb` operation
* Force conversion to sRGB for CMYK images with ICC profile
  CMYK is not supported by PNG, WEBP, AVIF and HEIC Pillow encoders.

  When a CMYK image is encoded, it is converted to RGB but this conversion results in inaccurate colors because Pillow ignores the ICC profile when performing the conversion.

  As a workaround, we manually force an accurate conversion to RGB _before_ encoding the image. This results in a much more accurate representation of the original CMYK image.

Especially useful when dynamically creating favicons.

Note: `wagtail.ico` is taken from wagtail.org.