[Gameplay] Slow-immune champions are not affected by Singed's Goo Fling

This has been a long-standing bug for Singed (since Singed has gotten the ability to snare enemies by flinging them into his goo, I believe) and I'm just reporting it after a game where it felt helpless to do anything against a fed Yi because Singed's only hard cc that doesn't hold himself in place is bugged against Yi when he's ulting. While I have not tested it myself, I've heard this happens to Sejuani as well when she's slow Immune, so I'm quite certain that is the condition under which this bug occurs. Obviously, since this is a snare it should work against these champions, but since the snare is applied at the same time as the slow/grounding, I am assuming it cancels both out instead of just the one.

This is a very big bug that is a big problem in specific matchups, and it has existed for over half a year now. I would very much like to see this bug fixed before another half of a year passes.