ci: use Alpine Linux instead of Arch as base image

While running a CI job, the following error was thrown:

	checking keyring...
	downloading required keys...
	:: Import PGP key B8AC08600F108CDF, "Jan Alexander Steffens (heftig) <heftig@archlinux.org>"? [Y/n]
	checking package integrity...
	:: File /var/cache/pacman/pkg/zlib-1:1.3-2-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
	Do you want to delete it? [Y/n] error: zlib: signature from "Levente Polyak (anthraxx) <levente@leventepolyak.net>" is unknown trust
	error: failed to commit transaction (invalid or corrupted package)
	Errors occurred, no packages were upgraded.
	Cleaning up project directory and file based variables
	00:01
	ERROR: Job failed: exit code 1

Use Alpine Linux for the libinput job for stability.

Fixes: #6


Signed-off-by: José Expósito <jose.exposito89@gmail.com>