Agree that hardocding is a sucky way to do it. Sorry my suggestion was from memory. Looks like you need to do something more like what you see on https://learn.getgrav.org/content/media#url for the same effect.
If you learn a little about the debugging tools available in Grav, you should be able to get the right expression if that doesn’t work. I’d rather point you to that so you can understand and help yourself better in future.
BTW what happens when you try to load your SVG file directly in your browser? I know a little about SVG from a while ago, but not about browser support. It hardly had any when I messed with it!