I had a similar 1/8″ sidewall cut with a scuff that flexed too much for Stan’s to seal. I glued a regular small patch to the inside of the tire after cleaning the area thoroughly. It was still fine when I replaced the tire almost a year later.
In case the previous two posts weren’t enough to convince you, a regular inner tube patch applied to the inside of the tyre wil work great. Just check that when pumped up to pressure the tyre doesn’t bulge too much as it will attract more abrasion and wear.