Bump alpine to 3.21 #2429

Job	Run time
alpine:3.21 / Build alpine:3.21 - generic - core - amd64	5m 16s
ubuntu:24.04 / Build ubuntu:24.04 - generic - core - amd64	7m 2s
alpine:3.21 / encryption-remote-https-bad-cert	7m 48s
alpine:3.21 / encryption-remote-static	9m 52s
alpine:3.21 / encryption-remote-https-pinned	9m 8s
alpine:3.21 / encryption-local	9m 59s
ubuntu:24.04 / encryption-remote-static	15m 3s
ubuntu:24.04 / encryption-remote-https-pinned	14m 37s
alpine:3.21 / encryption-remote-auto	10m 10s
ubuntu:24.04 / encryption-remote-https-bad-cert	10m 17s
ubuntu:24.04 / encryption-local	13m 7s
alpine:3.21 / acceptance	10m 55s
ubuntu:24.04 / bundles	8m 40s
ubuntu:24.04 / encryption-remote-auto	14m 0s
alpine:3.21 / custom-partitioning	9m 4s
alpine:3.21 / install-target	10m 55s
alpine:3.21 / install	10m 55s
alpine:3.21 / reset	9m 1s
alpine:3.21 / upgrade-with-cli	10m 59s
ubuntu:24.04 / acceptance	10m 54s
ubuntu:24.04 / custom-partitioning	9m 15s
ubuntu:24.04 / install-target	11m 8s
ubuntu:24.04 / install	10m 54s
ubuntu:24.04 / reset	9m 43s
ubuntu:24.04 / upgrade-latest	2m 9s
ubuntu:24.04 / upgrade-with-cli	1m 29s
alpine:3.21 / upgrade-latest	1m 10s
ubuntu:24.04 / install - SecureBoot	1m 48s
ubuntu:24.04 / zfs	1m 2s
alpine:3.21 / netboot	16m 8s
ubuntu:24.04 / netboot	6m 48s
	4h 39m 16s

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