SwifterPM 0.8.13 uses SwiftPM artifact scratch path for restores

The pinned swifterpm dependency is bumped from 0.8.12 to 0.8.13 (revision 39bf0b3). 0.8.13 uses SwiftPM’s artifact scratch path when restoring packages, fixing restore path handling instead of relying on an unreleased swifterpm revision.