GH Actions: cygwin: Use incremental archives for the sage-local artifact #30154
Description
Only store modified/added files that were not in the previous stages.
https://www.gnu.org/software/tar/manual/html_node/Incremental-Dumps.html#incremental_002dop
CC: @dimpase @embray @slel @kliem
Component: porting: Cygwin
Author: Matthias Koeppe
Branch/Commit: 5ccf1ea
Reviewer: Jonathan Kliem
Issue created by migration from https://trac.sagemath.org/ticket/30154