sign: switch to SHA2-256 signature by default #3004

Job	Run time
Build melange and add to artifact cache	39s
Build packages (bubblewrap, hello-wolfi)	1m 29s
Build packages (bubblewrap, glibc)	13m 31s
Build packages (bubblewrap, tini)	1m 24s
Build packages (bubblewrap, lzo)	1m 26s
Build packages (bubblewrap, bubblewrap)	1m 12s
Build packages (bubblewrap, gitsign)	2m 53s
Build packages (bubblewrap, guac)	4m 6s
Build packages (bubblewrap, mdbook)	3m 49s
Build packages (bubblewrap, s3cmd)	1m 22s
Build packages (bubblewrap, perl-yaml-syck)	1m 25s
Build packages (bubblewrap, ncurses)	2m 16s
Build packages (qemu, hello-wolfi)	1m 51s
Build packages (qemu, glibc)	13m 48s
Build packages (qemu, tini)	1m 55s
Build packages (qemu, lzo)	1m 59s
Build packages (qemu, bubblewrap)	1m 44s
Build packages (qemu, gitsign)	3m 15s
Build packages (qemu, guac)	4m 46s
Build packages (qemu, mdbook)	4m 31s
Build packages (qemu, s3cmd)	1m 50s
Build packages (qemu, perl-yaml-syck)	1m 43s
Build packages (qemu, ncurses)	2m 34s
	1h 15m 28s

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