fix: Update AltSign to fix Windows IPA permission errors (#447) (#1315)

Update AltSign to include Windows IPA permissions fix

Bumps the AltSign submodule to SideStore/AltSign#13, which makes
unzipArchiveAtURL: fall back to 0644 when a ZIP entry carries no Unix
mode bits (as produced by Windows zip tooling). Previously these
entries extracted with mode 0000 and failed during signing with a
"You don't have permission" error.

Fixes #447

Author: mikey820