Right now, the avatar for the GitHub @wikimedia organization badly contrasts with the dark background (avatar background is #26292f), and only appears properly on a white background. This is mainly due to the transparency that was not removed on upload:

{F37727626}

Since the dark background is widely used on GitHub, it's probably worth adding in a white background to the image to always ensure that it's on a white background, instead of relying on the page's CSS setting the background to white (which is only the case when light mode is used). I'm suggesting a white background since foundation:Legal:Visual identity guidelines#18 (and a few other parts of that page) implies that the mark must only be on white backgrounds.

I've attached a possible replacement avatar below. The mark currently appears smaller than what the GitHub organization avatar currently has, as I padded the logo with more space to comply with the clear space requirement in foundation:Legal:Visual identity guidelines#16.