Looks like this is an extension :) You dont place it in the scripts folder you instead do one of the following:
1)double click the aseprite extension file provided to install.
2)open aseprite and drop the file provided in to asepeite to install
3)install by opening the preference menu located under edit>prefernces> Extensions click on the button to install the extension and navigate to where you've downloaded it 😀
Hopefully this helps!!
Just a reminder that extensions are installed like this where as scripts are usually dropped in the folder like you were saying. Extensions are the way to go as they are easier to manage as the user, I still have a few of mine I need to convert to extension though xD But yes just be sure to look if it's a script or an extension is all and you should ne good to go! :D