Dockerfile: bump Alpine from 3.20.0 to 3.22.1

[ee7]

See release posts for 3.21.0, 3.22.0, and 3.22.1:

• https://www.alpinelinux.org/posts/Alpine-3.21.0-released.html
• https://www.alpinelinux.org/posts/Alpine-3.22.0-released.html
• https://www.alpinelinux.org/posts/Alpine-3.19.8-3.20.7-3.21.4-3.22.1-released.html

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Previous bump: #99