But it’s just an image link to some SVG file. No HTML involved, only a Markdown image link that GitHub will render as an HTML <img src="…"/> element. The actual SVG file linked to isn’t even necessarily hosted by GitHub.
And, getting back to the original point, you wouldn’t be worrying that GitHub doesn’t “support” a URL that happens to point to a file of a particular subformat that the URL itself doesn’t disclose.