dockerfile: update Alpine to 3.18

[crazy-max]

Also update Alpine edge digest.

[crazy-max]

Ah now I recall why we pinned to 3.17 moby/moby#44570 but seems this one is new: https://github.com/moby/buildkit/actions/runs/5416169191/jobs/9845520595?pr=3976#step:8:981

 > [dnsname 3/3] RUN --mount=target=/root/.cache,type=cache   set -e; make binaries; mv bin/dnsname /usr/bin/dnsname:
0.361 GO111MODULE=on go build -mod=vendor -ldflags '-X main.gitCommit=18822f9a4fb35d1349eb256f4cd2bfd372474d84' -o bin/dnsname github.com/containers/dnsname/plugins/meta/dnsname
30.08 # runtime/cgo
30.08 In file included from _cgo_export.c:3:
30.08 /usr/include/fortify/stdlib.h:23:15: fatal error: stdlib.h: No such file or directory
30.08    23 | #include_next <stdlib.h>
30.08       |               ^~~~~~~~~~
30.08 compilation terminated.
67.01 make: *** [Makefile:42: binaries] Error 1

[tonistiigi]

@crazy-max This was in some other repo as well. Something with musl-dev needs to be added manually now.

[thaJeztah]

Ah, yes; related (same issue);

• Dockerfile: update ALPINE_VERSION to 3.18 docker/cli#4354