Fix multiple AT files not working when final file name matches

[pupnewfster]

Currently for cases like Mekanism where we have multiple mods separated by sourceset but different submods may need additional AT files that have to be named accesstransformer.cfg so that they work in prod the AT generation is broken as it overrides the copies of the AT files with the last file. For example:

minecraft {
    accessTransformers {
        files(
                file('src/main/resources/META-INF/accesstransformer.cfg'),
                file('src/additions/resources/META-INF/accesstransformer.cfg')
        )
    }
}

Was only outputting a single file to build/neoForm/neoFormJoined1.20.2-20231019.002635/accesstransformers/User/accesstransformer.cfg which contained additions' ATs but not the base ones. This PR makes it so that it creates a second file in that folder called accesstransformer_1.cfg so that then when passing them along it can apply both of them. This is a similar solution as what is done for creating the task's name