Check the casing. If it hasn't severed into that I'd say it'll be fine.
I packed shoegoo into a 12mm cut on a Vittoria Randonneur that I rode for a couple thousand miles afterwards without incident. The differences there being the Randonneur was a seriously tough tyre and the cut was lengthwise on it...yours is across it on I believe a lightweight tyre.
See what happens I guess. It's on the rear so at worst you'll have one hell of a corner drifting session if it blows
I could do without the drifting session to be honest, I'm not sure my rims would appreciate it
The Shoe Goo should arrive mid week but I've just ordered a new tire as well... I'll probably keep riding it until the glue arrives then whip it off and inspect it. If it's worth repairing I'll fix it and put it back on, keeping the new tire as a spare. If I can see any damage to the carcass I'll bin it and use the new one